Rover 200 & 400 Owners Club • Battery charging Auto electrician advice needed
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Battery charging Auto electrician advice needed

Posted: Tue Sep 16, 2025 4:31 pm
by Bean66
Hi All

Slighhtly off the wall question to any knowlegable auto electricians out there.

My 25SW battery keeps going flat.

Reasonably simple reason, it generally does short journeys so not enough charging and can sit for weeks without being used.

Now ages ago I saw a solar charger that purportedly plugged into the cigarette lighter and charged the battery as long as it was light, tho obvs more in the sun.

So couple of questions.

Would such a thing even work?

I don’t suppose it provides much power but as long as it partly offsets the draw from the alarm system and delays the batt going flat that would be a good thing.

I kind of assuming that as its providing a small current into the system that is enough to power or partly power the alarm system meaning less draw on the battery and maybe charge the battery, even a bit.

However I’m assuming IF it does or would work it would need a cigarette lighter that was permanently live as if it was only live with the IGN on the circuit would be broken with the IGN off.

So has anyone heard of such and thing and would/could it work?

Cheers Bean

Re: Battery charging Auto electrician advice needed

Posted: Thu Sep 18, 2025 5:49 pm
by CoupeFan
In my experience, the alarm system can run the battery flat if the car is left unused for 3-4 weeks.

I now use a compact charger that I bought in Halfords some time ago. It can recharge a battery and then when it is fully charged it automatically switches to maintenance mode to keep it topped up. It came with 2 sets of fly leads, one with traditional croc clips, the other with loop terminals that go on the battery terminal clamp nut & bolt. Each fly lead ends in a 2pin connector which plugs in to the lead from the charger unit. The loop terminal flyleads are intended for use with a motor cycle where the battery isn't as easy to access as on a car. But they can still be used safely with a car.

I have the loop terminal leads permanently connected to the battery terminal clamp bolts. When I want to top up the battery all I have to do is open the bonnet, connect the fly lead in the car to the lead from the charger unit and plug the charger unit in to the mains socket.

The only electrical knowledge needed was to connect the loop terminal with the red sleeve to the red +ve battery clamp and the loop with the black sleeve to the - ve battery clamp.

I have made myself a small sign that sits in front of the speedo, I put it in place when I put the car on to charge to remind me to disconnect the charger before I try to start the car or drive it.

I appreciate this isn't an answer to your exact question about a solar powered charger that connects to the cigarette lighter, but there's no need to mess around with the interior or the cigar lighter and its wiring.

Re: Battery charging Auto electrician advice needed

Posted: Sun Sep 21, 2025 1:53 am
by Bean66
Hi Keith

Appreciate the comments.

I do pretty much the same tho i'm not sure my battery lasts that long.

I just wanted to get rid of the faff of getting the charger and extension cable out and setting it all up every couple of weeks, thats of course if i remember to do that before it won't start again. :laughing2

I just don't know if the solar panel idea would work.

Cheers Bean

Re: Battery charging Auto electrician advice needed

Posted: Sun Sep 21, 2025 6:41 am
by Topcat Tomcat
Bean66 wrote: Sun Sep 21, 2025 1:53 am
I just wanted to get rid of the faff of getting the charger and extension cable out and setting it all up every couple of weeks, thats of course if i remember to do that before it won't start again. :laughing2

I just don't know if the solar panel idea would work.

Cheers Bean

I've often wondered about the solar panel possibility, as I have four cars needing regular charging.......and my memory isn't what it used to be.

The trouble is, I'm a born sceptic, and as it seems too easy a solution, I've never followed it up!

Re: Battery charging Auto electrician advice needed

Posted: Sun Sep 21, 2025 1:52 pm
by CoupeFan
Bean66 wrote: Sun Sep 21, 2025 1:53 am Hi Keith

Appreciate the comments.

I do pretty much the same tho i'm not sure my battery lasts that long.

I just wanted to get rid of the faff of getting the charger and extension cable out and setting it all up every couple of weeks, thats of course if i remember to do that before it won't start again. :laughing2

I just don't know if the solar panel idea would work.

Cheers Bean
I deeply sympathise. My car was off the road for 15 years in total because it was in a flat battery/flat tyre loop. I have a mains supply in my garage and a short extension lead so that there's always power within 2 feet of the front of the car. If your garage doesn't have a 13 amp socket or the car isn't garaged then I can see the attractions of a solar-powered charger.

There is no reason why a properly made solar-powered charger wouldn't work, after all, it is just a source of electricity. But it would need to be made specifically for the job. I'm not sure if on cloudy days it's the voltage that drops, or the current, or both. But that's why it would need to be a purpose-built dedicated product from a reputable supplier. Halfords sell them, and there are several on ebay (other online sites and sellers are available) which claim to be able to do the job.

The illustrations show them as also having croc clips, so if it's digging out the charger and the extension lead that's the problem then you'd just attach the croc clips to the battery terminals and if the car's outside and the lead's long enough you should be able to put the solar array inside the car and close the door and bonnet carefully, making sure that you don't nip the cable between the bonnet, door, and the body.

Feeding the power from the charger through the cigarette lighter would, as you say, mean that it would have to become an unswitched feed from the battery, which used to be the case when cigar lighters first became standard equipment. It's only in the last 10-20 years that the lighter socket has been on a switched feed through the ignition to avoid anything plugged in to the lighter socket draining the battery whilst the car's parked - been there, done, that, got the T-shirt, and received GBH of the ear'oles from "she who must be obeyed" the following morning, we were on holiday at the time........

If you still want to use the lighter socket as the feed in from the solar charger then you must disconnect the lighter socket feed and replace that with a wire with, most importantly, an in-line fuse next to the battery direct from the red/+ve battery terminal to the lighter socket. But you will need to get to the back of the lighter socket to disconnect the existing wire, and make sure that you tape over the connector on that wire so that it cannot come into contact with anything metal or electrical once it's free of the lighter socket.

Here is a photo of a lighter socket for a Rover, not too sure if it's for a Metro/100 or a Coupe, or, for that matter why I have it.
WIN_20250921_14_30_25_Pro.jpg
Note there are 3 terminals, 2 on the socket itself, and one on the illuminated surround, which has an additional spring contact, you can just see it, to the metal body of the socket. The single terminal on the surround is fed through the lighting switch so that it lights up when you put the lights on, and you shouldn't need to touch that.

If you do go ahead and run a dedicated wire from the battery to the socket you will need to terminate it with a push-on female spade connector with an insulated boot and that goes on the terminal in the centre of the socket. The terminal to the side of the centre terminal is the earth contact. You will need to make up a short flylead with a female push-on spade connector, with insulated boot, at one end, and a flat male push-in spade connector at the other end. One end of this flylead with the push-on female connector goes to the side terminal on the socket, the other end with the push-in male spade you push into the corresponding side socket on the plug that you removed from the back of the lighter socket. This restores the earth connection to the socket. You can get spade connectors from Halfords, but take care when selecting the bubble packs from the peg hooks in the shop as the spade connectors do come in different sizes.

You will also need a suitable loop terminal, Halfords call them ring connectors, so that you can securely attach the new wire to the bolt on the battery clamp, and the piece of wire itself, automotive wire capable of carrying 15 amps should be more than adequate as you will be fitting a 10 amp in-line fuse, Do not use mains cable.

WARNING: Don't forget, you ABSOLUTELY MUST fit an in-line fuse carrier in this direct wire close to the battery, a 10 amp in-line fuse should be more than adequate. if you don't and for any reason the direct wire chafes and causes a short the resulting high current could start a fire or possibly make the battery suddenly overheat due to the short and explode. Also, make sure that where the wire goes through the bulkhead there is a grommet protecting the edges of the hole to stop the edges of the hole from chafing the insulation on the wire. The fuse will also protect the battery in case the solar charger becomes faulty, or something else that you plug in to the now-permanently live lighter socket has a fault/becomes faulty in use, or, heaven forbid, someone accidentally puts a piece of metal or tinfoil into the socket and shorts it.

You'll also need to remember that the socket is now permanently live and leaving anything plugged in that uses current when you leave the car could mean that you have a flat battery when you next go to use it, just as I/we did all those years ago.

This shouldn't be too difficult to do, the hardest part will be getting to the back of the lighter socket.

I haven't worked on car electrics for some time, other than sorting out a recent issue with the boot light not working on my Tomcat. In my younger days I used to love working on car electrics and was a dab hand, even though I say so myself, at fitting fog lights, both front and back, reversing lights, clocks, air horns, burglar alarms, car radios, electric aerials, cassette players, trip computers, additional instruments/substitute instrument panels, etc. to a Triumph Herald, a Jaguar XJ6, Austin 1100, 3 different Allegros, a Morris Marina, a Morris 1800S, a Princess, and 4 different Metros.

Re: Battery charging Auto electrician advice needed

Posted: Mon Sep 22, 2025 8:56 pm
by Bean66
Hi Keith

Cheers for that.

My car sits outside so attaching a battery charger means getting the extension out and putting it through the front door, which is the bit thats the pain and difficult to do for overnight charging or taking the battery off the car, more of a pain, esp as the front drivers door lock doesn't like the key and obvs with no battery the C-Locking doesn't work.

The solution is simple of my wifes TF as i've fitted a screw off battery isolator, so most of the time the battery is disconnected. But with the TF i can lock the car and easily get the the battery to remove/fit the screw in isolator connector as the bonnet release is in the boot which is opened by the key, not so simple in the SW due to the key issue.

But I've been doing more reading round on the subject and yes it is/should be feasable to do the solar panel thing.

But, and there is always one or more, its possible to overcharge the battery and ruin it by constantly charging with an unregulated supply, any supply including a solar panel.

So it seems all batery chargers, including trickle charger battery conditioners have a Charge Controller Regulator to stop overcharging.

Now I’ve no idea how long it would take to ruin a battery using a solar panel but I’d rather not find out, so i'll need to add one of those into the system, which means its going to be slightly more involved wiring it all in semi permanently.

I think I have a choice, sort the driver door lock so I can easily use a key and fit an isolator, this might be a good idea anyway as if the battery 100% fails its difficult to get in the car using the key, or sort the solar panel thing properly, including find the battery draw with the car just sitting there. This would be useful to find out if my current 15w solar panel is up to job of keeping the battery topped up with the car sitting there.

Cheers Bean

Re: Battery charging Auto electrician advice needed

Posted: Mon Sep 22, 2025 9:32 pm
by CoupeFan
So you already have a solar panel. Is it specifically designed for recharging a car battery? Does it automatically switch to a low current "Maintenance" mode when the battery is fully charged? If the answer to either question is "No", or "Don't Know" then I personally would be very reluctant to use it because of the risk of damage by prolonged charging.

That is why you need a purpose built solar charger designed for the task which automatically switches to Maintenance mode when the battery is fully charged.

The solar charger will produce very little power at night, possibly not even enough to offset the current taken by the alarm. So that reduces the chance of overcharging. But I still would only use a purpose built one designed to recharge a car battery that had automatic switching to Maintenance mode.