Li-SOCL2 cells

[Daravon]

At work we have LCD tags that are currently powered by lithium primary cells. The battery cost is eating us up, and I need to either find a source of cheap lithium primaries or make a case for switching to rechargeables.

I looked at the cells we are using now and there are 3 different brands. Two of them are 14500 size and one is Size A, so apparently size A can fit our device. The 14500 ones only last a month and the size A one lasts 6 months. Some of them say LI-SOCL2 cells; all of them say "do not recharge" and "3.6V".

Does anyone know a good cheap/bulk place to buy size A and/or 14500 primary lithiums? Why shouldn't we switch to rechargeable lithiums? What is life of a rechargeable lithium compared to these primaries in this kind of low-draw application, and what is the total life (so I can compare total cost compared to primaries)?

I know rechargeable lithium cells are popular with flashlights nowadays but I have not personally used them...I stick to Nimh and CR123 primaries.

 

[tobrien]

did you check www.batteryjunction.com ?

they've got legit everything insofar as battery sizes go. you may want to measure the size of those "A" batteries and see if it's just a manufacturers name for a more well-known battery standard we're all familiar with haha

 

[CKOD]

Rechargeable lithiums may or may not work because of the voltage. Li-SOCl2 cells are meant for low drain long term storage. If youre only lasting a month, then its not really the low drain that they are meant for. The datasheet for a random LiSOCl2 AA cell I pulled up has a discharge curves that run from 55 hours out to almost 8 years.

LiMnO2 primary cells may be a better choice if the slightly lower voltage still works. Can you measure the voltage of the current cells after they come out? The battery life with a Li-MnO2 cell may not be better, but they should be a good bit cheaper than the current cells. Battery junction has AA LiMnO2 cells.

 

[Daravon]

Rechargeable lithiums are also 3.6V, aren't they?

The "dead" batteries measure 3.68V with a multimeter, but if you place them in the tag and measure them in-circuit, they get drawn down to 3.4 something volts. So it appears the tag needs 3.5 volts at least.

 

[CKOD]

Most likely a LiMnO2 cell wont work then, they start off a little under 3.6v and are ~3.0 V under load. Li-Ion rechargeable may be worth a shot then. They are 3.7v nominal, and 4.2v fully charged. LiSOCl2 cells have a pretty flat 3.6v discharge curve. As long as they play nice with 4.2v with the fully charged cells, draining them down to 3.5v wont be that hard on the Li-Ion cells, so the cycle life of the cells should be pretty long. Since youre looking at ~700mAh then, youre presumably looking at changing the batteries twice as often, but given that an AW 14500 costs $10, and a LiSOCl2 AA costs ~$6, your ROI, including charger(s) should be quick.

 

[bestsystem]

try 3 1.2V Ni-MH cells:party: