Let's get him in the ballpark before you go all high tech on him! Yes, he's got a dirty connection or two to deal with that are dropping too much voltage. A series resistance check and individual voltage drop measurement of every connection can come in due time. I'd suggest a specific gravity check over the next several weeks with monitoring of the electrolyte level to establish the optimum voltage setting to keep the battery charged without losing an excessive amount of water. That's how we kept 40-something batteries at peak efficiency in the fleet I maintained several years ago.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!