Battery charging amps vs time

[awol]

I am trying to work out actual battery used by the length of charge time.
My watt meter tells me my trip to work, taking it easy cost 2.5ah (for example).
My battery is a 36V 10ah bottle battery and my charger is a bmsbattery emc120 stating 42v 2.5amp
Am I to assume that my 2.5ah trip should take 1hr to charge with the 2.5a charger? is that how it should work?
I am noticing a pattern where the charge time is generally taking approx 2x my estimated charging time based on
2.5a per hour charging so am maybe suspecting the accuracy of my watt meter or I am working it out wrong.

 

[KirstinS]

Some chargers taper the charge toward the end so , for example charge at 1a between 4v and 4.10v and then slides down to 0.5a between 4.1 and 4.2v

No idea if your dies this though - I'm sure somebody will though

This could throw off your numbers maybe ?

Also maybe efficiency losses as well 20 -30% are figures I've seen bandied about

 

[Deleted member 4366]

Make an adater to connect your wattmeter between your battery and charger. Then you will see what's happening. It should show 2.5a when you first plug in.

 

[awol]

A great idea d8veh. Took me a while to get my head round the wiring but it works a treat, I didn't realize you could do that.
Also it showed KirstinS is correct with the charge amps tapering down as charge goes in which has answered my question as to why it takes more time to charge and also that my watt meter seems accurate. Thanks.