Looking at these again to keep a car battery 'just' good enough to start without a jump.  For a Golf rather than a Focus but batteries are the same size and both EFB.

Charging with the Maypole and a powerbank was a waste of time and hassle as the battery was too flat to start without a jump again after around 2 weeks.  I know the battery is damaged internally, but no point replacing it unless the car is going to be driven regularly again.  My current diagnostic software doesn't support this car either as it's too new, so I wouldn't be able to code in a new battery if I did replace it.  Unsure whether that would cause any issues or not on this car.

I do still have an AA panel, which I considered putting back in.  But it's only 2.4Watts and a quick look online shows they now make panels rated at 10W and 15W and higher...  Interested to know whether anyone is using one of the modern higher rated panels and whether they do work more effectively to maintain a battery above 12v?

Thanks

If we lived in Florida or even Spain then there would be a reasonable possibility that a Solar battery maintainer could work.

Since we live in cold grey Britain and for most of the year we can expect 10 hours of daylight or less meaning  solar chargers are of limited benefit.

Now in ideal conditions a 15W panel could in theory provide a charge current of just over one Amp which would be useful. In reality you could probably expect around 700mA on a bright day. As we approach winter the hours of meaningful daylight will get progressively less, so the solar panel will only be providing a charge current for 6 or 7 hours.

For the solar panel to be of real use in the UK, in winter, I think you would need at least a 40W panel. They are available and very often used with caravans but the down side is the size of them.

5 hours ago, unofix said:

Since we live in cold grey Britain and for most of the year we can expect 10 hours of daylight or less meaning  solar chargers are of limited benefit.

OMG! Have you passed this little known and vital information to Mr Miliband?😀

I have used 20W foldable solar panel just to keep the battery voltage at level, since Focus was parked for a week or longer. It worked well. Plug in to the cigarette lighter plug, unfolded in the morning, folded in the evening..no problems. For a battery maintenance, even slight charging, foldable panels of 25-30W are more than enough. 100W is a bit of a money waste.

I have put the AA panel back in for now.  Got overwhelmed with all the choice on Amazon earlier.

Don't think lighter socket type works on the Golf.  I believe the sockets are not powered without the ignition on, but should check that.  The AA panel uses an OBD plug.

When you say folded in the e being and unfolded in the morning, do you mean you were manually moving it every day?  That's not an option for me, I need something I can just leave in place for months at a time.

32 minutes ago, Ned_Mk2_1.8tdci said:

For a battery maintenance, even slight charging, foldable panels of 25-30W are more than enough.

What country are you in ? 🤔

So here's something interesting...  Two weeks after the AA solar panel was plugged in, just tried it, no battery warnings, car started immediately, no jump start needed!

Perhaps that's an unfair test as it may have got some extra charge during the MOT beforehand, but I will leave it plugged in for another 2 weeks to test now.  I was fully expecting it to need jumping and to put the AA panel on the charityshop pile!

I have a 20W panel which is about the size of an A3 sheet of paper that I hang in the windscreen.  This only really produces 15W max but has been enough to keep my battery topped up for months at a time when not using my mini digger.  Maybe not a true test for a Ford Focus as there are no electronics to drain the battery when switched off.

Let us know how it goes after another 2 weeks.

35 minutes ago, south_bound said:

Maybe not a true test for a Ford Focus as there are no electronics to drain the battery when switched off.

What country are you in ? 🤔

He means the digger has no electronics to drain the battery, I think.

3 minutes ago, mjt said:

He means the digger has no electronics to drain the battery

I understand that.

I would still like to know his geographical location since the effectiveness of a 20W solar panel in the UK, in winter, is about as much use a chocolate teapot. 😉

1 hour ago, unofix said:

as much use a chocolate teapot.

I'm sure they'd be fine for iced tea!.

Seriously, it would be good if we could find one that did do the job of topping up rather than messing about with the smart charger every now and then. 

And solar power has the support of the Government, so it must be good!😀

8 minutes ago, Eric Bloodaxe said:

And solar power has the support of the Government

Would we be able to get an electric car subsidy if we chuck a solar panel on the dashboard?

I wonder whether there's enough difference between the 'amount' of sun in southern UK compared to Northern UK to make solar chargers slightly more viable down here?

Even on a dull, drizzly day the charger still seems to be providing just over 12v.  I don't have a clamp-meter to check amps unfortunately.

1 hour ago, TomsFocus said:

Even on a dull, drizzly day the charger still seems to be providing just over 12v.  I don't have a clamp-meter to check amps unfortunately.

The absolute minimum voltage you would require to stop the discharge from the battery would be 12.65V. Note I don't say that 12.65V would actually charge a 12V car battery.

To measure the current flow from the solar panel to the battery would require a multimeter set on the mA range connected in series. The current flow would be too small to measure with a general purpose clamp meter.

I'm not against the idea of using a solar panel to keep the battery topped up, in fact I would use one myself to keep our Vauxhall Movano horsebox battery in tip top condition. However you should always immediately half any quoted value of a solar panel since even in perfect conditions, you won't get more than 12 hours of light. So a 20W panel will at best only give a maximum of 10 Watts in any 24 hour period. That's hardly enough power to keep a 5W bulb illuminated for a full day.

At one time Nissan experimented with having a Solar roof on the Leaf to see if that would extend the range. Unfortunately the additional weight and the necessary associated  equipment needed actually reduced the range in all but a few European countries. It did kind of work in Spain but the amount of power generated didn't make it a viable project. I know trying to power an EV from solar is not the same as trying to charge a regular battery but you can see the problem, you need a large solar panel in good sunny/bright conditions to get a useful amount of power.

The AA panel is plugged in via the OBD port so can't add a multimeter in series unfortunately.  All I can say is the battery quickly dropped to 11.7/11.8v before.  But hovers just above 12v with the panel plugged in even on  dull day, so it must be doing 'something'.  This does seem to be enough for my needs at the moment.

It is hassle having to unplug & replug every time I want to start the engine though, as the OBD port is quite low down on the Golf and the angle makes it awkward to fit by feel as well, so even this is not an ideal solution.  But it is better than having to thread cables through from the dash to the battery terminals each time.

5 hours ago, unofix said:

the effectiveness of a 20W solar panel in the UK, in winter, is about as much use a chocolate teapot

This is one of my gripes about covering thousands of acres of productive agricultural land with solar farms. They produce least output in the winter when demand is highest and most in the summer when demand is lowest. I do wonder if the idiot Milliband has the slightest knowledge of the basic physics.

The situation is the same with air-sourced heat pumps.

1 hour ago, mjt said:

I do wonder if the idiot Milliband has the slightest knowledge of the basic physics.

Probably has the same level of knowledge on solar as he has on how to eat a bacon sandwich 🐖

On 9/16/2025 at 5:07 PM, unofix said:

What country are you in ? 🤔

Fair question, it will produce more solar power in south of France than in northern England!  It does produce even on cloudy days but obviously not as much and nowhere near what it is rated at.  I measure 14V and about 1A (so 12W) in the sun and less in cloud.  It works for what I need it for though.

1 hour ago, south_bound said:

Fair question

But you still didn't answer it 🤣

13 hours ago, unofix said:

But you still didn't answer it 🤣

I gave two locations and one of them isn't in the UK😎

Quick update.  Only been one week since previous start as I decided to service the car in the hope of sealing the leaking fuel filter.

Car started fine, then did another couple of starts as can't quite work out whether the filter lid is still weeping, lots of doors and boot open and closed as I cleaned the interior while I was out there.  No battery warnings so far.  I know this battery is damaged as it wouldn't charge above 12.2v on the Maypole before, but the AA panel is obviously doing something so will keep that plugged in for the foreseeable.  I am hoping to attempt short drives, or even just shunting around the car park, over the next few months, so will hopefully be 'using' the car more than before if that does happen.

In other news, I have since confirmed that I can't code a battery for this car for free/cheap.  The 7 year old software that I used for the older one doesn't cover later models.  And although there are a couple of generic OBD tools that will do it, it's looking like £50-£80 to buy the adapter and credits/licence for 1 year where applicable.  Not worth it when the battery would only cost around £80.  So I would have to leave it uncoded (effectively no BMS reset) if I do change it myself.

5 weeks later...  Engine still started!  I can't explain the science behind it but the solar panel is definitely working at the moment.  

Sadly my optimism from a few months ago has been superceded by reality now.  There's no longer any chance of me driving the car any time soon.  I will still try to run the engine once a month though, and if the solar panel saves me having to get the jump starter out every time, that's a plus to me.