Lithium starter batteries

Goran · #1 5th May 2015, 08:27 AM

Just found this new lithium starter battery, they seem to be getting cheaper.
https://store.starkpower.com/12V36Ah...GER-_p_57.html

This one is 36Ah Lead acid equivalent, but usually that translates into a real capacity of 18Ah roughly.

Which should not matter because of the restart technology always leaving enough juice in the battery to start the car.

Only 2kg too!

snapdragon · #2 5th May 2015, 02:50 PM

Would be good on the VW Phaeton that has a separate battery for starter and comfort. Not sure what our battery managers would make of it though!

Cornershop · #3 27th May 2015, 09:15 PM

Quote:

Originally Posted by Goran

Just found this new lithium starter battery, they seem to be getting cheaper.
https://store.starkpower.com/12V36Ah...GER-_p_57.html

This one is 36Ah Lead acid equivalent, but usually that translates into a real capacity of 18Ah roughly.

Which should not matter because of the restart technology always leaving enough juice in the battery to start the car.

Only 2kg too!

I enquired about a uk dealer as I've been thinking one for the 911 - said they'd get in touch with uk dealer details but nothing yet.

Adrian E · #4 27th May 2015, 10:20 PM

LiFePo should be OK for starter duties - LiPo doesn't like being deep discharged and is a bit like a live grenade if mishandled! The ferrite versions are lower voltage and generally don't mind a bit of abuse. Not sure it's worth the aggro unless your car is on a serious diet though?

Cornershop · #5 28th May 2015, 07:07 AM

Quote:

Originally Posted by Adrian E

LiFePo should be OK for starter duties - LiPo doesn't like being deep discharged and is a bit like a live grenade if mishandled! The ferrite versions are lower voltage and generally don't mind a bit of abuse. Not sure it's worth the aggro unless your car is on a serious diet though?

My 911 is lighter than a standard G50/1987 car with f/g bumpers, sunroof delete, recaro furious, rear seat delete, plastic rear light clusters, ally clutch housing, but not what I call serious. Maybe 75kg saved, which isn't too bad in a car that weighs 1200kg standard.

Standard battery is 18kg so if I can loose another 12-15kg and add some useful functionality like BMS, it's worth it to me as my lockup has no power.

snapdragon · #6 30th May 2015, 06:54 PM

If it was me I would get a small AGM due to tolerance of repeated deep cycle and fast charge rate but smaller and lighter.

Goran · #7 1st June 2015, 08:31 PM

Some Porsches already get LiFePo4 starter batteries as standard.
In my opinion LiFePo4 with a battery management circuit is much more suited as a starter battery than any previous battery technologies. After all a starter motor is almost like a mini EV motor, it draws a large current to drive a heavy load. I don't see any EVs going back to Lead acid (be it AGM or not), NiCd or NiMh.

With a low voltage cut-off circuit it should theoretically never be damaged by over discharging.
If the cell management circuit lasts, once you pay the first-time higher cost of a battery with a management circuit, when the cells eventually become useless you can replace just the cells with another set of cells for probably around the same price as a Lead Acid starter battery. I think I saw A123 Systems 20Ah prismatic cells for £25 each, and you only need 4 cells. These are good quality cells not the cheap stuff.

Here's mine, around 30Ah, installed in December I think, so far I'm very happy with it. It hasn't gone into low-voltage cutoff yet even sitting for 7 days. The car really likes the higher voltage of the battery, much nicer starting. I just need to install a proper bracket to hold it down, I'm risking stressing the cables at the moment. The smaller cables taped off, in the background, are the remenants of windscreen heating, I haven't got round to removing them completely.
I bought it from the States, no problem air-shipping at that time, but laws may have changed now.

snapdragon · #8 2nd June 2015, 08:06 AM

Interesting Goran. How many volts is it? Does the voltage drop much when cranking? I find lead acid go down to ~11v when cranking.

Goran · #9 2nd June 2015, 10:06 AM

I'll check it next time when I start the car. I suspect it shouldn't drop too much if my experience with other Lithium batteries is anything to go by.
Normally it sits at around 13.2 to 13.3V when connected and boot open (so boot light on).
The 110Ah lead acid battery used to sit around 12.0 to 12.2V when I kept checking it, but it wasn't in good shape, even at only 2 years old!

Goran · #10 3rd June 2015, 09:32 PM

Here's a quick test. This battery also goes down to 11V briefly when cranking.
Depending on which source you believe 13.15V for 4 cells is around 50% to 60% state of charge. Probably equivalent to a Lead Acid battery at 12.2V to 12.25V
Not bad for a tiny 30Ah battery?

https://youtu.be/9tn8EEt0uWQ