What deep cycle battery to charge car "main" battery

[Shnozz]

My Lotus lives in an underground car park with no access to power nor sunlight. In winter months this presents a battery issue.

I bought a Ctek CS Free but its not up to the task, frankly. I can, however, use it as a pass-thru between a second battery and the car battery. The second battery can then be removed periodically to be recharged and then connected back up.

Any recommendations for a deep cycle battery? Was thinking of limiting this to 80A for weight purposes so its not too heavy to lug back and forth when needing a recharge every month or so.

[charltjr]

I’m guessing you’ve already considered it, but curious as to why you’d not use a battery cutoff instead?

[Shnozz]

charltjr said:

I m guessing you ve already considered it, but curious as to why you d not use a battery cutoff instead?

I would like the alarm and immobiliser active, as well as the central locking. I have also found modern cars tend to be more prone to throwing a wobbly when not connected for a while. Add to that the reset of stereo settings and clocks, and the final issue is the negative terminal to which a cut off would be fitted is in the most inaccessible place imaginable on an Exige, sufficiently so I think you would need to unbolt the retaining clamp to be able to reach it. You can just about get a battery clamp on the top of the neg terminal using some body contortion.

[Weekendrebuild]

Definetly purchase a property with a garage this sounds like a pain. Saving that I’d just get a cut off they aren’t that hard to get to an you can get remote ones.

[CABC]

I get the modern cars don't like to be disconnected, but Lotus/Toyota seem resilient in this regard. There is far less ancillary stuff to get "confused" and the core EMU is solid. I still disconnect my Toyota many times a year, no issues. Fancy modern car from last 10 years, nope.

over on SELOC Arno has described a reliable system. uses the DC Optimate charger and leisure battery.

[Shnozz]

Soooooo, can anyone actually, you know, recommend a decent deep cycle leisure battery?

Not that I’m surprised by the answers thus far, being PH…

[MDT]

Shnozz said:

Soooooo, can anyone actually, you know, recommend a decent deep cycle leisure battery?

if you are to be carrying it about, I would suggest you look at getting a LiFePO4 battery, as they are much lighter (like 0.5kg), and these like the one below can take lots of cycles and they can handle being run totally flat without causing any damage.

https://www.amazon.co.uk/12V-100Ah-LiFePO4-Battery...

[gotoPzero]

Yep 100A Lifepo4 - you will need the correct BMW and charger for it too and ensure you balance charge it and keep it healthy.
Another option is a power station like ecoflow.

[Shnozz]

Thanks chaps.

Will my trusty old "standard" 3 pin charger work on these or does it need one of these sort of fancier ones?

https://www.amazon.co.uk/ECO-WORTHY-LiFePO4-Batter...

[MDT]

Shnozz said:

Thanks chaps.

Will my trusty old "standard" 3 pin charger work on these or does it need one of these sort of fancier ones?

https://www.amazon.co.uk/ECO-WORTHY-LiFePO4-Batter...

sorry..... you need said fancy one. hope Santa pops one under the tree for you.

[gotoPzero]

Yep as above you need a specific Lifepo4 charger.

Also if you are unfamiliar with that chemistry then be aware you should never fully discharge the battery - if you buy a good quality battery it will have an internal battery management system which will prevent over discharge. If you do fully discharge it can cause serious damage to the battery.

Also its advised to fully charge the battery too which allows the cells to balance.