Non-mains trickle chargers?

[Starjet99]

I have a car that I use fairly infrequently, especially in the winter and during lockdown. After two weeks standing, the battery - which is a nearly new 100Ah - is reading around 12.1v, which I assume is related to ongoing battery drain from running the cars systems. The model of car is quite known for this and also very sensitive to battery voltage.

I'm looking at ways to keep the battery healthy. Unfortunately, the car isn't kept close to a mains power source, so a CTEK device is out.

I've looked at solar powered trickle chargers, but realistically how effective are they? Is there any other non-mains options, aside from removing the battery and charging it indoors? This would be a bit of a faff, and would mean resetting the car's systems all the time so is not my preferred option!

[Collectingbrass]

I use a solar charger that plugs into the ODB port, this one

I prefer this over anything that connects direct to the battery as all the wiring is kept inside the car. While I don't have any battery data they seem to work fine, the cars (a Z4 3.0 & an Alpina D4) start with no fuss no matter how long they've been stood.

[Miserablegit]

It’s not discharged yet but doing some simple maths:
14days 100Ah used
1day 7.14Ah
An hourly drain of about 0.3Ah so whatever you connect it to will need to provide this as a minimum.
12v * 0.3= 3.6W so a solar panel could do it
Alternatively, buy two more batteries of the same type and charge them at home, connecting one of them up at a time to the existing battery. That will give you more time between charges

[CABC]

20w optimate solar chrg with charge controller, that way 20w is probably ok for winter and controller prevents overcharging in summer. The silly little £20 panels don’t give enough.

[finlo]

CABC said:

20w optimate solar chrg with charge controller, that way 20w is probably ok for winter and controller prevents overcharging in summer. The silly little £20 panels don’t give enough.

This is what I ended up doing as the little 5w one couldn't keep up.

[Starjet99]

Thanks, chaps.

Solar it is! Halfords to a 6W solar panel which I might try, and if that doesn't do the business, I'll return it and go for a heftier Optimate 20W instead.

The battery is in the boot, so the panel can sit in the parcel shelf with the wires fed through to the battery easily enough.

[paintman]

Had a play with a small one a few years ago.
Fine in good sunlight. Total waste of time in winter.
Suggest you go with finlo & CABC,

[GreenV8S]

You'll need around 20 Wh per day to compensate for the typical residual draw.

Don't take the nominal power ratings of these solar panels at face value. By the time you account for latitude, daylight hours, clouds, other shadows, non-optimal angles and so on you might only get 1% of the claimed output on average.

[E-bmw]

Starjet99 said:

After two weeks standing, the battery is reading around 12.1v,

That is flatter than a flat thing!

A 12 volt batter is actually 6 x 2.1 volt cells in series and every 0.1 volt under 12.6 is a loss of around 20% of its total charge, so 12.1 is about 20% charged.

[Starjet99]

E-bmw said:

That is flatter than a flat thing!

A 12 volt batter is actually 6 x 2.1 volt cells in series and every 0.1 volt under 12.6 is a loss of around 20% of its total charge, so 12.1 is about 20% charged.

Perhaps I just need to use the car more!?

Reading 14.4v with the engine on. The v8 fired up with absolutely no hesitation... didn't feel in any way flat!

[Angpozzuto]

I'm using one of these on my MK1 MR2 with a battery drain
https://www.amazon.co.uk/dp/B081CYQ97B?ref=ppx_pop...