Trying to squeeze a little additional service out of a weak battery is false economy at its finest. Possible unintended consequences include damaging your alternator and starter, damaging to the vehicle due to excessive outgassing and boilovers, and getting stranded at an inconvenient time or place.

A typical battery has a monthly cost of that is less than the cost of a couple quarts of diesel fuel. Not exactly great savings potential; even less if the battery is covered under a prorated warranty.