The charger's which come with these lead acid AgM battery packs are just basic single voltage wall wart style transformers.
They are NOT ideal for charging a battery, any battery, and arguably cannot fully charge a battery. They are little more than 'maintainers' with a low output and low voltage.
With an AGM battery, when the current required to hold it at a high absorption voltage falls below 1% of the capacity( 20 hr rate) then it can be considered fully charged or very nearly so
I have taken one of these jumper packs which have been on the charger for a week, and put them on my adjustable voltage charger, and the 12AH battery within took another 3.4 AH at 14.8 volts before amperage dropped below 0.012A.
So this battery which had been sitting plugged in on a single stage 13.6v charger for a week+, was not more than 70% charged, and was never going to get more than 70% charged on the provided charger, and the battery was going to degrade much faster when chronically undercharged.
These small capacity AgM batteries are pretty cheap, and widespread, and hardly a high quality battery. More mass produced [censored] from overseas. Their amp ratings as stated by the jumper pack marketers, have absolutely no correlation to CCA figures that come included on starter batteries or marine batteries.
If you have smaller amperage automatic charger available, you can hook it to these jumper packs and recharge the battery better than the included single stage 13.6v wall wart transformer that it came with.
But even those will likely stop well short of a true full charge. If you do not have the tools to measure Amp flow at absorption voltage, you are absolutely blind as to battery state of charge on an AGM battery.
The blinking green light that says any given battery is indeed fully charged, is mocking your intelligence, and rightfully so, if you believe it.