The 7400 deck mount converter is a single stage at 13.8v which is fine for regular converting such as on shore power, but is very slow as a battery charger.
There are more modern converters that are less money and are also better (faster) at battery charging and also offer a lower float voltage 13.2 vs 13.8 (if you are floating at 80F ambient -13.8 is for 50F ambient)
So don't replace that 7400 with another one at any price. Get a converter with more features. There are several choices to pick from to match your camping situation.
We can each tell you our favourite brand for that situation if you tell us what it is
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1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.