Buy a Hydrometer and....safety glasses....rubber gloves....and a big box of baking soda. Keep water hose handy and wear your old clothes just in case.
Trust me on the safety part....I use to fill batteries in my youth, nothing to be complacent about those however harmless they may look to some.
$20.00 meters from CT are more than good enough for what most of us will do with them. Good warranty anyway at CT....
I think they do have a low battery warning, I guess I'll have to read the manual(s) if ever again I get strange readings. Or ride next door and borrow his really good one.
Mind you....I have never counted my meters, I have a few, one permanently with the bike's tools. All good enough for what they are.And one to mount in the dash, very bad things can happen on my bike if attempting to start it with a low battery. Bad as in....very expensive to fix.No letting that "Magic Smoke" escape....
Not much need for them with an Odissey battery altough I have done the tests with the battery left connected untendered for 5-6 weeks. All good....!
And much safer to handle.
If, and only if, you go for the cheap(er) CT meter, try the switch in the store, that's what broke on mine twice. One never even worked right out the box, the other one failed early but you can tell if the switch action isn't smooth at first. The other twos.....no problems in 3+ years just have to remember to keep a good battery in there and turn them off after use.
Motors....batteries.....and maybe even meters, nothing should really sit for a long time and yes 6 months is a long time, without some preventive maintenance, much cheaper and lots less aggravating that way.