Charing problem

[miken7132]

Have a 6v positive ground system with a generator/cutout (battery less than a year old, new NuRex cutout). Starting with the battery at full charge, after driving about a mile the charge drops to 65% to 70%. Ran the battery, ground, and cutout tests in Les Andrews' Troubleshooting manual - everything passed. Ammeter shows 10 amps when running, 0 with the engine turned off. Appreciate any ideas as to why the battery is losing charge.