Amp/hrs vs. Amp/min....

[DANO]

Hello All...as it says, why two formats?  Oviously you could do the math and figure out what you're dealing with but....why?  Here's my question and it's about true "deep cycle" vs. the in between "marine/rv" types.  From what I see out there, the deep cycles are rated in amp/hrs at a 20 amp/hr discharge rate, whereas the marine/rv units are rated in amp/minutes @ 23 amp/hr discharge...no industry standard?  Does this mean that a T105 will last 225 hours (not!) vs the marine/rv with a rating of 225 minutes equaling 3.75 hours (225min divided by 60).  I needed to vent on this, pardon the pun....Any observations/advise...

[AbyssUnderground]

The 20 hour rate refers to the capacity divided by 20 = the amps you can use for 20 hours and get the full capacity out of the battery.

EG

200Ah / 20hours = 10A > You can draw 10Amps for 20 hours before 0% state of charge is reached.

You should divide the 10A value by 4 because you dont want to discharge past 25% if the battery is to last a longer than a few months.

[Opera House]

My understanding was that the 23A figure was based on a typical automotive draw, how long you could drive a vehicle at night with a failed alternator.