specific gravity readings for batteries
 

during a trip to sears to pick up a battery charger/starter, i also picked up a specific gravity measuring tool. i have been having problems with my batteries due to lack of use, so i thought i would post the readings of both cars.

Car # 1 -- '73 911E - 2 batteries (before a charge):

#1 1180 #2 1100
1180 1180
1180 1165
1180 1170
1190 1175
1175 1180

battery #2 had one cell that was reading very low (1100), and the rest were in the "recharge" range of the SG device.

couple of things to consider: a few months ago, i added distilled water to all of the cells as they seemed a bit low. i had charged them last weekend, started the car (after many, many cranks), and taken it for a 50 mile drive after parking it for a week.

i recall seeing a post from Early S Man in which he stated that the passenger side battery usually shows a lower SG readings that the driver side one due to the proximity to the starter. i can't tell which battery was the passenger side because i didn't label them until a few weeks ago.

in any event, it looks like these batteries can't hold a charge very well, and one looks like it has a dead cell??

Car # 2 -- '89 911 -- 2 year old battery, drained several times due to lack of driving the car,

before a charge:

1165, 1165, 1170, 1175, 1165, 1165

after a 1 hour 20 amp charge (automatically shut off by charging unit):

1180, 1180, 1190, 1170, 1180, 1165

some cells got better, but some got worse. in all cases, the SG reading was still in the "recharge" range.

so my questions is: are all my batteries toast?

Are they all dead? Perhaps only one out of the three. Batteries don't like being cycled too many times. Cycling is when a battery discharges, then recharges and so on. Stuff flakes off of the cells during the discharge/recharge cycle and builds up inside the battery case where it can eventually cause the plates to short out. In other words, keep batteries fully charged for maximum life.

SG readings should be fairly uniform between cells. As you suspect, #2 battery in car #1 seems destined for major paper-weight duty.

Before condemning the other batteries, make sure they are charged and able to create a high-enough SG. Charging a discharged battery for only an hour (even at 20 A) may not be long enough to recharge a partially sulfated (discharged) battery - better to charge it for several hours (overnight is good) @ low current levels to see whether it's merely discharged (normal) or ready for the scrap dealer (unable to hold a charge).

If you don't drive the pcars that often, consider using a battery maintainer between uses, and if you value your pcar, consider using a sealed battery to avoid reducing the chassis weight via battery acid corrosion.

This website has pretty good information about batteries.

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars