Wal mart marketing.
The standard rte of battery capacity measurement is at a 20 hour rate. a 5 amp load for 20 hours until battery voltage drops to 10.5v means it is a 100 amp hour battery.
A group 27 will be anywhere from 100 to 115 amp hours but I would lean towards 100.
I have personal experience with t a very similar schumacher charger to the one you show.
The thing's voltage reading is very inaccurate. Mine was 0.25 volts away from actual at 12 amps and 0.65 volts off at 25 amps output. Also the button which one can push which states the state of charge as a percentage, well this is voltage based and quite inaccurate, especially idf the voltage is no where near accurate.
Marine cranking amps is measured at a higher temperature than cold cranking amps.
Your battery is good enough for your intentions. You have it on a charger, you are doing the right thing.
If you use the battery a lot with the engine off, just put it back on the charger when you get home.
I do have to warn you about these schumacher chargers though. Sometimes they will go upto ridiculously high voltages, Mine would/will regularly shoot up past 16.4 volts and this is abusive. This behavior is widely reported on these chargers all over the internet.
The occassional blast upto 16.4 on an abused battery might be an OK thing to get it back to true full charge, but not every single timeit is plugged in.
I recommend not leaving it unattended especially if it is wired into the vehicle while charging.
I also recommend getting a cheap digital multimeter.
Harbor freight sells a good enough digitial multimeter for checking resitance and voltage. Sometimes they give it away free with purchase of something else or coupon.
https://www.harborfreight.com/7-function-multimeter-98025.html
A more functional digital multimeter is the clamp on ACDC ammeter. When clamped over any single wire, it can show how many amps are flowing through that wire. This is very useful in terms of figuring out how much load is on the battery, like from a fan, or how much amperage a charging source is delivering.
Such as if your battery was accepting 10 amps at 12.7 volts, it is no where near fully charged. If it was accepting 1 amp at 14.7 volts it would be very close to fully charged.
Here is an inexpensive DC clampmeter that I have no personal experience with:
https://www.amazon.com/Signstek-UT2...rd_wg=tFgRz&psc=1&refRID=2BXXNGGS9N8GRY4J6FWR
Any cheaper and it might only measure AC amps, instead of both AC and DC.
Without knowing the amperage flowing, voltage can be quite useless, but knowing how many amps are
flowing at that voltage, in or out of thebattery, can be quite enlightening.
Wal might sell a group 29 which is an inch longer than the group 27, and is basically the same as a group 31, but no matter now.
If that charger goes to float soon, I'd recommend unplugging it, replugging it in, and put it on AGM setting and let it go overnight. it will drop again to float voltage, but instead of 13.2v it will stay at 13.7v and this is more likely to squeeze in the last few percent of charge.
These chargers usually stop a bit shy of 100% charged. Once in float there is no risk of it shooting back upto 16.4v+, that only occurs before 'float'
I'd not leav ethe battery plugged in for 2 weeks on AGM setting in hot ambient tmeperatures, but overnight is fine on the AGM setting.
The AGM setting might also keep the 16.4v masochistic schumacher episode from occurring.
My schumacher of similar appearance is from 2007, Its display no longer works. It is undependable. i don;t trust it on any battery I care about without monitoring it.