There are no upgrades for the batteries AFAIK. You just have to be conservative with them (you can only go at flank speed for a little under an hour on battery power). Generally you don't want to go over 1/3 in the vicinity of an escort, 2/3 if you're only forced under by an aircraft.
__________________
"Men who flinch not with the fathometer ticking off two fathoms beneath the keel … Men who will fight to the last bullet and then start throwing the empty shell cases. These are submariners"
-Eugene Fluckey
|