Working on the 1983 Foretravel Hendrickson Chassis with 6V92 power. The Battery box at the far left rear measures approximately 23"X24". Does anybody have any knowledge of what batteries were originally installed. Some of us think 2 8D and some think 1 8D and three Group 31. Either config fits but the hold down frame looks like it was modified later to accommodate the 3 Group 31s. We have to do all new battery cables so we have some freedom to be creative.
Look for the combination of the most CCA (Cold Cranking Amps) and reasonable price.
Be sure the CCA of your battery bank meets DD's minimum for your engine.
You can get actual battery dimensions from most battery manufacturers/marketers.
I had no problems with (3) 24 series but went to (3) 31 series. About 2900 CCA and $300 for all three Duralast Autozone. Ask for discount. 24s lasted about ten years. 2900 CCA far exceeds the Detroit requirements.
Our fire trucks used 2 8D batteries. One won't do the trick.
Pierce