Lithium 12V batteries in Think

[Zuikkis]

Hi,

I have seen some of you are using lithium batteries as 12V battery. What are your long term opinions?

Think always seems to drain the 12V battery if not used for a few months. It doesn't help that the battery is in so impossible location that you can't easily remove the cable so it wouldn't drain. However it should be possible to add a "main switch" with extended wires, perhaps to the minus terminal..

Anyway, I now have two cars both with dead batteries. Cheapest suitable lead acid battery is about 50€ in Biltema. (about 550 NOK)

Then there is for example this lithium battery for 65€ :
https://www.motonet.fi/tuote/fulbat-litium-akku-12-v-387-wh-fltx4l5l7l-fltz5s6s7s?product=90-02092

but some obvious questions,

Only 3Ah! Is it enough? The stock lead acid is 45Ah or something like that. But I guess just starting the car doesn't really use that much. However you must perhaps avoid listening to radio or leaving lights on unless car is fully awake.

Does it work in winter? It can't be charged below 0C, but then again the main battery has the same limitation and seems to charge just fine.

[Zuikkis]

Oh, another thought occurred. Does PCU supply 12V when external power (230VAC) is available and charging starts? What I mean, if the integrated BMS inside 12V lithium battery disconnects the battery for protection (too cold or low voltage etc), is it possible to wake the car up by connecting charging cable?

[worry]

Hi,
I tried using the same, a 3Ah lithium battery from Biltema. Weight only 1 kg!

The starting amps is more than enough to start, but I experienced empty battery after about 5-7 days. I think I wrote something about it on the thread for my red Think project. Measured the drain amps, which seemed to be normal.

Too much hazzle, so I went back to a standard lead acid battery. No problems now.

Yes, the PCU delivers 12V "charging" while charging the HV battery. At least mine does. Ca 14,2 volts. Read somewhere that the capacity of the HV to 12V transformer is 100 amps.

[Zuikkis]

The starting amps is more than enough to start, but I experienced empty battery after about 5-7 days. I think I wrote something about it on the thread for my red Think project. Measured the drain amps, which seemed to be normal.

Ah. Well this sort of matches my lead acid experience? Fully charged 50Ah battery is deep discharged beyond recovery in about two months.. So there must be some drain.

I figured that even if Lifepo4 would drain, it wouldn't ruin it because the BMS cuts the battery when it gets too low voltage. But perhaps it's better to invest in main switch, so car can be completely shut down easily.

Something like this from biltema:
https://www.biltema.fi/autoilu---mp/sahkojarjestelma/virrankatkaisijat/paavirtakytkin-100-a-2000016429

[Orbit]

I think it would be better to install a contactor/relay close to the battery, and only run a low amperage control line to a convenient switch positon. This avoids running thick cables plus a high amperage fuse (which also implies that a short on that cabling still can do signficant damage before the fuse blows).

[Zuikkis]

I think it would be better to install a contactor/relay close to the battery, and only run a low amperage control line to a convenient switch positon. This avoids running thick cables plus a high amperage fuse (which also implies that a short on that cabling still can do signficant damage before the fuse blows).

In my other car projects, I have often placed the battery main switch on the minus side. Then there is really no risk of short circuit, as short circuit would simply be the same as turning the switch on. And you can find the actual chassis ground point near to the switch, so the wires are reasonably short! Plus side would have to go twice the length to get back to the battery.

Speaking of the 12V battery, this new Think had very different looking battery mount to my earlier Thinks. This is a two piece design. You just open a few M6 bolts and the bottom drops out, together with the battery. There is enough loose on the cables so you can then remove them quite easily. Much better than the older(?) one piece mount..