Charging System/overhaul questions from bad alternator

[docbob]

It is not unknown, but not necessarily common, that old regulators will not work with new/rebuilt alternators. The voltage limiter adjustment in the regulator is, ideally, adjusted to meet the requirements of the specific airplane. Often these can be CAREFULLY adjusted to work with new alternators. This is the ONLY adjustment that I know of on the transistorized regulators.

The Cessna Charging System Manual lists the following as probable cause for a discharged battery:
-Charging circuit resistance too high (loose or dirty connections, for example)
-Voltage limiter malfunction or low setting (could be)
-Accessory load too high (doesn't sound like your probloem)
-Corroded or loose battery cable connectors (probably not but I'd check anyway)
-Metal chips in field relay core gap (I suppose?)
I'm wondering if the alternators were installed correctly and were ever working at all. Depending on the circumstances is is not impossible that a new battery could work for 3 hours. What did the ammeter and/or voltmeter tell you?
I'd do everything simple first then attack the regulators.
Good luck, Bob