[tfj]

Could someone outline how to charge the mini9 from a car charger?
I bought a used mini9, arriving fully-charged and apparently working fine. At present I don't have ready access to a 120-volt outlet. I bought an $8
"19 Volt 1.58 Amp" car-charger ('precisely' the mini9's official specs), and when I connect it to an old AGM-lead battery (which reads more like 11 than 12 volts, but is still usable), it measures at 17.5 open volts, and when connected to the mini9, it starts out at maybe 0.3 amps, but within about ten seconds rises to 2, maybe 3 or more amps, the mini9 battery LED then turns on orange and starts blinking, and the current suddenly drops to zero. No obvious damage done.
I'm somewhat ignorant - What would be wrong with this charger that would cause this behavior? Or does this indicate something wrong with the battery, or the mini9? Can you suggest some tests?
Should a more expensive charger work (and what necessary specs should I look for)?
I don't want to use a DC-AC converter. Thank you, tfj
The user manual doesn't seem to give any detail about charging (e.g., what signals does the battery LED send?).