Honda HRR2169VLA ... electrical / battery specs help

Hi all, this is my first post and I am hoping for some recommendations.

I bought the above Honda walk behind used from a Honda / JD dealer and have maybe 1 hour on it since buying it a month ago. It's a 2013 with electric start and is in pretty good condition with what appears to be average hours. When I bought it, the electric starter needed to be replaced as the starter drive gear would not engage the flywheel. I tossed the new starter on today and it started without much issue, but it still didnt seem like it was getting the juice it needed. Didn't think much of it as it hadn't been used much and figured by the time I was done mowing, it would've recharged fully.

Today was my first actual mowing of my .3 acre yard and towards the end, I found the battery was struggling to get power to the starter. I noticed this as I had to empty the bag three times and started it with the electric start each time. After all my mowing was done, I turned the mower off and came back to it about 10 mins later and tried to start it with the electric start just to see if it would...and it BARELY had enough juice to fire up.

I did a little diagnosing of the electrical system and these were my findings:

• With the battery removed, it was sitting consistently at about 11.9 volts.
• With the battery removed and the mower running, I was getting about 12.1 volts at the connectors.
• With the battery in and the meter on the terminals, when cranking over it dropped to about 6-6.5 volts.

So, now I question whether my mower is providing adequate charge to replenish the battery....OR is the battery just in need of a solid 24 hour charge using Honda's charger...OR is the battery just flat out shot? I suspect it's the battery, since the mower is putting out 12.1 volts, which seems sufficient to recharge. I am by no means an expert on electrical systems, so I'll open it up to your thoughts / expertise. Anyone know how many volts the mower should be putting out to sufficiently recharge the battery? FYI, the battery appears to be the original.

Thanks for your help!

First Charge battery for at least 12 hours. Should be 12.4 or higher
Charging systems put out 13 to 14 volts and battery should never drop that low when starting.
You should not go by the battery being removed to tell if charging. Connect battery, turn on mower then check voltage at battery at full speed. Could have auto sensing built into charging system. Don't think so but it is a Honda and you never know.

Your 3rd test is poor man's load test. Bat should not have dropped to that v during test. If you can access electrolyte (bat fluid) thru caps use a bat hydrometer (cheap, $3 any auto store) . Buy one with small nipple to fit down into bat fluid holes. Charge like Blaz says and take a hydrometer reading. A terminal voltage test is not always significant as bad bats can have a surface charge of 12 v.