45 amps for 25 minutes is roughly 33.33 amp/hr (about 1/2 of what you should have in a 75 ah battery.)
45 amps for 17 minutes is roughly 22.66 amp/hr (about 1/3 of what you should have.)
While there is some derating (Peukert number) that will make a battery deliver less amp/hr at high amp draw, 45 amps is not a particularly high discharge rate, so you should be getting at least an hour of run time at 45 amps (to full discharge). My estimate is that these batteries are at their end-of-life for an EV, but could probably be used as IC starting batteries a while longer.
Peukert Number Battery Life Calculator
That being said, your starting voltage was rather low. At 12.5 volts, you were starting at about 90% of charge - but just an estimate - hard to tell actual 'charge' without a hydrometer. If your batteries measured 12.5 volts after being charged, they have problems - perhaps your charger isn't doing a good job? - just something else to check. The charger should be putting out just over 120 volts at the end of the charge cycle (for a 96v pack of flooded batteries.)
Running a battery to 'dead' is really hard on the battery - Kind of like having a heart attack - you can only have so many before things don't recover... If you drive it to 'dead' every day, your pack probably won't last more than a few months.
If your batteries were new, you should be getting around 1.5 to 2 miles 'per battery' out of your pack to about 80% discharge (because they are relatively small amp-hr wise) on flat roads. I'd expect you should see 10 to 15 miles of range with eight 12v/75 ah batteries (much less if you have to go uphill...)
Even one bad battery can make range really poor. Since you appear to have two mostly bad ones, that probably explains why the 5 miles. When you do replace batteries, don't buy them one at a time - you'll have fewer headaches with batteries that are all the same age.