Contributed by: Ray Calvo
This article was prompted by a few experiences of trying to start the 993 on weekends; it seemed that over a week's period the battery would go dead. A little checking indicated that the battery was dying - several cells were bad. Although the battery is approaching 4 years old, I think this was largely caused by neglecting the check of the electrolyte level periodically; at least two cells (the bad ones) were uncovered, and the others were pretty low. Adding distilled water and recharging for a few days did not restore them.
HINT - PORSCHE BATTERIES ARE GENERALLY NOT SEALED UNITS; YOU HAVE TO ADD WATER TO THEM PERIODICALLY. I don't know if this is true on the latest cars, but my '95 993 has a battery that looked very similar to the one in my '84 Carrera - white plastic with a screw-in cover for each of the 6 battery cells (each cover has an indented "+" in it). To unscrew the cover, I used a 1" wide cold chisel - had a larger blade than a regular screwdriver and avoided stipping the indented slots. Water level should be no lower than the little tabs sticking down inside the cells; definitely the metal battery cells should be covered. Use only distilled water for this.
If you suspect a problem, you can have the battery checked at a shop; they'll largely do a load test to determine the amperage capacity. At home you can also check the electrolyte charge in each cell with a hydrometer; all cells should be equal and in the green zone on the hydrometer.
If you need a new battery, shop around and get the proper type. Note the mounting system on the original; the battery is held in place by the extruding flange at the bottom of the battery. On 911s from about 1974 at least, this flange fits into a channel in the car body, and then a clamp on the opposite side of the battery secures it in place. Many of the US batteries do NOT have this flange. For info, the battery type for the 993 (and I believe for all 911s since about 1984) is a group size 48. I purchased an after market unit of this size that matched the original mounting perfectly.
One problem I have
noticed universally is that when you replace a battery, you lose the station
presets in the radio. Also, I have heard some rumors (not substantiated)
about inadvertent actuation of the airbags due to voltage/current surges
when changing a battery. To attempt to avoid these potential problems,
I did an experiment. I have one of these regulated trickle chargers
that are supposed to keep the battery at the specified voltage/charge level
during long-term storage. I hooked it up across the cable terminals
such that it will supply power to the car even with the battery disconnected.
I then removed the battery, ran to the store, got a new one, ran back,
and installed the new battery. The trickle charger kept a constant
power supply to the car, and I never lost my preset radio stations.