Cordless Battery Trickle Charger?

[SentientBean]

Evening, fellow Lemon Possets

Does anyone know if there is such a thing as a cordless / battery powered trickle-charger for a 12v wet cell car battery?

I’ve scoured the internet for hours and cannot find anything, so I’m guessing not, and that there must be a scientific / physics reason for this I guess.

The problem I have is my wife only drives her RAV4 about once or twice a week these days, and then for only a few miles at low speed / low revs in local traffic. It only gets a longer run (1hr+ at sustained speed / higher revs) about once a month. So usual story. Once winter comes around, even with a new or newish battery, after a couple weeks or so of freezing temps the battery is not dead flat, but low enough not to start (11.70v or less).

I have one of those Li-Ion boost start packs which are excellent, gets it fired up under 3 mins. And then take the car for a 60-90 min run on dual-carriageway / motorway to get battery back to 12.68v

Have to do this 3 or 4 times over winter, then once into spring / summer / autumn generally don’t have the problem. Though do go through a new battery every 2-3 years vs 5-6. But alternator is kicking out good / normal charge. Battery is holding charge (plus it’s only 12 months old). Had both verified by AA service tech. I don’t think there is an excessive parasitic key-off drain (though I’m now monitoring). Only started having this issue 2-3 years ago when the wife started using the car much less. Prior to that never had any battery issues for years. So I’m associating low usage with small battery capacity (it’s a stock spec 330 CCA / 45aH type, where-as my own car has equally low usage but a 750 CCA / 74aH battery and I don’t have the same problem).

I could just keep up this routine, even though a tad tedious. However, I’ve read multiple times that it really isn’t good for the battery or the alternator (which I’m more concerned about) to be using the car to get back from a sub 12v (<25%) charge to a 12.68v / 100% charge regularly.

Problem is, the car is kept in an underground garage, where there are no (practical) options to use a mains powered trickle-charger. And no sunlight (or even bright enough artificial light) to use a solar powered trickle charger.

Not only is removing the battery on the RAV4 (well this model, circa 2003) a right pain in the a** as requires removing windscreen cowling. But also the car REALLY doesn’t like having the battery removed and gets amnesia on engine management system / ECU et al (aside from the tolerable stuff like losing all radio and sat-nav data). It takes a good couple of days to re-learn it’s optimum idling / fuel use etc, meanwhile constantly stalling (it’s an auto-box!) and really pi**ing off the Mrs, for which I get ear-ache. So removing the battery to trickle charge inside home (or even a second one and hot-swapping) is not really an option I want to pursue on a monthly basis, let alone more frequently.

Other than just running the car on pointless 30-40 mile loop for an hour every week, I was hoping I could find (or maybe even build?) a trickle-charger based on batteries (pref light-weight Li-Ion) which I could charge-up in the home, then place in the foot well and run a lead through closed window into bonnet and leave to maint trickle-charge the 12v car battery overnight once a week to keep it 100%.

Anyone have any ideas / suggestions / know if such a device is possible without having to hook up directly to a mains supply?

Many thanks

SB

[NomoneyNohoney]

So I’m associating low usage with small battery capacity (it’s a stock spec 330 CCA / 45aH type, where-as my own car has equally low usage but a 750 CCA / 74aH battery and I don’t have the same problem).


SB

I think you've answered it yourself. If your car with similar usage doesn't have the same problem, then upgrade to a bigger capacity battery, and that should solve it.

[bungeejumper]

Yes, as long as the battery tray will take a bigger battery (and I bet it will), that would be the better option.

There are, of course, rechargeable jump starters. This one seems to get good reviews: https://www.amazon.co.uk/Clarke-900-Sta ... op?ie=UTF8 . And apparently it does laptop batteries as an encore.

BJ

[stooz]

I think the solution is park it somewhere else where you have access to a trickle mains charger or a solar topup charger?

[richlist]

I've used a device called an 'optimate'. It keeps the battery fully charged by going thru a charge/ discharge cycle.......but you do need a mains power supply.

If you do get an alternative park space with power then an intimate is what you need.

[DrFfybes]

I've used a device called an 'optimate'. It keeps the battery fully charged by going thru a charge/ discharge cycle.......but you do need a mains power supply.

If you do get an alternative park space with power then an intimate is what you need.

You were doing so well until predictive text kicked in

[SentientBean]

Thanks to all who replied so far.

Yes, in an ideal world a mains trickle-charger with advanced regulator would be by far the best solution. But as it stands there's no way I can set this up regularly. The car could be moved and lashed up to the mains maybe once. But not regularly for logistical and security reason I won't bore everyone with.

I already have a portable jump-starter for the wife's car as an interim solution so she never gets stranded. And not one of the huge, old style wet-cell 10kg jobs. It's a small Li-Ion pack that fits in the glove-box, weighs less than 1kg and delivers up to 1000 cold crank amps for 5+ starts before needs recharging, and can hold full charge for over 6 months. It's been terrific. Can highly recommend. http://tinyurl.com/hbgnw5f

I was thus hoping to find a similar device (or something to work in conjunction with this - (inverter / regulator?)) which could be used as a portable trickle charger without the need for a mains outlet (or sunlight!).

I have indeed considered upgrading to a larger car battery, but it is a strange, very tight battery tray / placement, right against the firewall / bulkhead, and also has part of the windscreen wiper cowling over the top of it. So from initial scouring the web I'm not being offered any options for a heavy duty battery that will fit the space, just variations on the same type with a max CCA of 390, which is not much of an upgrade from 330CCA.

Does anyone know from a physics (or chemistry) perspective if a portable battery to battery trickle-charger device (with some form of regulator in-between) is even technically possible? - sounds like a market gap waiting to be filled to me!

Many thanks

SB

[iain123]

A battery powered ‘trickle’ charger is really just going to be the same as a bigger battery I guess? Your jump start kit sounds the best option other than that you could try a solar panel

https://www.amazon.co.uk/Visua-Powered- ... el+charger

and hope that the lighting in the underground car park would be enough – but like you already state its dull down there so probably not. Other than that you could securely mount an additional battery elsewhere in the car wired in parallel with the existing or try disconnecting any alarm system.

[NomoneyNohoney]

T

Does anyone know from a physics (or chemistry) perspective if a portable battery to battery trickle-charger device (with some form of regulator in-between) is even technically possible? - sounds like a market gap waiting to be filled to me!

Many thanks

SB

This web page http://www.powerstream.com/SLA.htm is interesting reading, particularly the section "DC Input Battery Chargers." The DC/DC taper charger that they mention seems to be what you're looking for, but finding one that doesn't cost $130.00 - ah! that may be your problem. Still, if I'm right, you know what to look for now. The direct link to their product is: http://www.powerstream.com/pst-pb1108.htm

[SentientBean]

Thanks for the suggestion and links NoMoney, that looks promising, will start there. Appreciated!

SB

[quelquod]

"If your car with similar usage doesn't have the same problem, then upgrade to a bigger capacity battery, and that should solve it.

You'd think so I suppose, but all things being equal a larger battery would surely just take proportionally longer before it went flat too. It's possible too that the charging system isn't so effective on the wife's car under these driving conditions.

[jfgw]

"If your car with similar usage doesn't have the same problem, then upgrade to a bigger capacity battery, and that should solve it.

You'd think so I suppose, but all things being equal a larger battery would surely just take proportionally longer before it went flat too. It's possible too that the charging system isn't so effective on the wife's car under these driving conditions.

A bigger battery will have more CCA and may start the car more quickly. I improved the starting performance of my first car considerably by fitting the higher capacity battery of the two recommended and getting a calcium one.

The CCA can vary a lot even for the same size battery. Checking ones for my own car (size 100), CCA(EN) values range from 570A to 760A. If the car takes a little while to start, it might be worth checking what CCA battery is fitted and, if possible, get something higher next time.

Julian F. G. W.