How long will it take to charge this battery with this charger? And why ("why" as in, what battery and charger specifications are used to determine the time it takes for it to charge and why?)
Thank you all very much.
Wild Feral guess: 7 Ah / .5 A = 14 + 30% = 18 hours (from totally dead). 
Charger is 500ma. http://www.upgi.com/media/2481/chargers.pdf
7ah battery / 0.5a charge = 14
So, 14 hours would be the best case for a full charge of a fully discharged battery. But, that’s a perfect world scenario that never happens. Battery heating, chemistry, ambient temperature, blah blah blah. Too many variables. 24-28 hours is probably a safe bet for all cases. Suffice it to say that if anybody gives you an absolute number with the data that’s been posted, it’s just a guess.
Worth a mention is that is a really basic, bare bones charger with no voltage control. A better unit will charge faster and extend battery life As a better charger will reduce the charge rate and thus the heat generated in the battery when charging is complete. A dumb charger just keeps dumping current, making heat which is the mortal enemy of any battery.
Thank you for the reply. That reminded me that the Li-Pos in RC cars can be overcharged and explode. I have another question. The battery has 7 amps, 20ah. Does that mean it lasts for 20 hours? I feel like it wouldn't always be the same because a more powerful device drawing more current would discharge it faster. Does it always take 20 hours to run out of charge? The battery will only run for a maximum of 30 min in total per day and it will be charging the rest of the time.
Thanks
PureStress:
The battery has 7 amps, 20ah. Does that mean it lasts for 20 hours?
The battery claims "12volt 7Ah/20HR"
Which means total capacity is 7Ah if you discharge it over a 20hour timespan.
So if you drain it in 20hours, you project can draw 7A/20hr = 0.35A = 350mA.
If you draw 7Amps, it SHOULD last one hour, but it doesn't.
Because losses are higher at higher currents.
But..., it's a common lead/acid/gel battery, and you shouldn't drain them more than 50% if you want them to last. Batteries like that are ok for backup systems (alarms/lights/computer UPS) but not suitable for daily 100% charge/discharge.
Leo..
So about how much current is lost from that 7 amps? 50%, 30%?
Depends on the current draw.
If you only draw 7Amp from a 7Ah battery, it shouldn't be that much less.
Good battery manufacturers have datasheets.
Leo..
PureStress:
The battery will only run for a maximum of 30 min in total per day and it will be charging the rest of the time.
How much current does it have to deliver for the 30 minutes that it will be running?
Steve
Hi,
What is the application?
Tom..
The drive motors will be drawing a total of 1 amp for 30 minutes at a time or 0.5 ah from the battery (this is the maximum length time scenario). There will also be a servo (specs unknown as of now), a motor-driven ball valve, and the Arduino of course. If I understand these posts this battery should work fine for the application.
What is the ball valve's motor Volts and Amps? How will you power and switch it? How will you power the servo? Post a wiring diagram?
And note that the nomial 7Ah is for a new battery at a particular temperature. As batteries age the capacity will reduce, and if abused the capacity will drop dramatically. As you only want 0.5Ah per day, regular charging
should mean a long battery life.
Abuse to avoid is over-discharge (permanently wrecks the battery), or over-charging (heats up and evaporates
the electrolyte.
Normally for a lead-acid battery you'd be hoping to see the phrase "deep-cycle" or "leisure" in the description so that
you are not being sold a vehicle battery. Vehicle batteries are designed for high peak current and being
kept fully charged at all times, not long life in a deep-discharge/recharge pattern.
Car battery charging time depends on many factors.
But,
Here the six most influential factors I am going to share with you.
- The Size Of The Battery
The most common facts, as you know.
If you want to charge your 48-Ah battery with a 2-amp charger, it will take 24 hours to charge fully.
If your battery size is 60-Ah, then it takes 30 hours to charge fully.
That means the bigger the battery more the time and the smaller the battery-less the time.
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