Now you've got me confused
I'm not understanding the first part...I think...
A battery does receive a healthy charge at first, then maintains the charge with lesser Amperage, if that's what you meant?
A small Amperage charger would probably re-charge your 100 Amp hour battery over the 5 day period...if you didn't discharge it too much while out, say, no more than 50%.
This way, it only has to replace 1/2 the capacity, only 50 Amp hours instead of 100.
Here is a link
to a charger FAQ. page.
Though more info than many may want, it does explain and answer just about any question there is about charging batteries, including the formula for how long it takes to charge a given Amp hour battery with a given Amperage.