I have a 24 volt trolling motor that was originally powered by two AC Delco M30HMF batteries hooked in series. One of the two batteries would not take a charge so I took it back to the dealer and he explained that the battery was no longer manufactured and offered to replace it with an AC Delco M29MF. The original batteries had 900 cold cranking amps and the replacement has 845 cold cranking amps. Will this be a problem? Both are charged by a Guest two bank charger. Thanks for any feedback.

Cold cranking amps do not matter for a trolling motor battery. Reserve Capacity (RC) is what you want. RC spec for the M30HMF is 180. If this is a warranty replacement, I wouldn't be happy if the replacement battery had less.

Check here, at the bottom of the list- they sell the M30HMF. I don't see any information about the M29MF. You might want to check the information you're getting.

http://www.batterysales.com/delco-pro.cfm