How long for battery to charge?

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Hi all. If it takes a 52ah battery 10 hours to charge how long will it take a 35ah battery to charge?
 
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I would say the battery is about 5 years old

A 5 year old might be like new, a six month old might have been abused. Put it on charge and wait whilst the 'charged' LED comes on, on the charger, then let us all know how long it took.
 
One of my older cars had an almost flat battery, using a CTEK 5amp took it a good 12-20hrs to charge and recondition.
 
One of my older cars had an almost flat battery, using a CTEK 5amp took it a good 12-20hrs to charge and recondition.

Quite right. My battery is an 80amp and I use a similar intelligent charger to the CTEK, rated I think 4.5a. It needs at least 24 hours to bring it back up to a full charge when its low. My charger might be rated 4.5a, but the current rapidly drops to below 1a as the battery begins to rise in voltage. The only way to more rapidly charge, is by increasing the output volts of the charger.

The difference in voltage between a flat battery on charge and one which is fully charged, is just a fraction of a volt.

I dumped all of my old fashioned uncontrolled, battery wrecking chargers long ago. The only way to check progress with those, was to watch the battery for gassing. Modern batteries are sealed, so just no way to observe the gassing. Leave them gassing too long and the battery was ruined.

Modern chargers can just be connected and left to it, with no risk of damage if they are forgotten about for an extra day or two, but if left permanently on charge, they are still quite capable of ruining a battery. I used to store my caravan in my drive, with its battery always on charge at 13.8v from its built in SMPSU. Two years of this treatment and it was ruined. My present regime is to put the battery on the 13.8v every month or two, for a couple of days at a time. Between times, it is isolated. When I intend to use it, I connect a CTEK type charger and bring it up to a full charge - I need a good battery for the caravan mover.
 
Hi all. If it takes a 52ah battery 10 hours to charge how long will it take a 35ah battery to charge?
10 hours.
Yes I know it seems daft but time is the main factor not charge rate. So with any lead acid battery as it discharges the sulphuric acid is turned into water and sulphur, and the sulphur is deposited on the battery plates, the longer the sulphur stays on the plates the harder it gets, so if you discharge a battery 20% and start the recharge one minute latter, then in one hour the battery is likely charged, but if you wait 8 hours then start to recharge then likely 10 hours, wait a month and likely will take a week to recharge.

It is not how fast the charger is, but how fast the battery will accept the charge. OK there are ways to recharge batteries faster, with a flooded lead acid (that means you can top up the electrolyte with distilled water) you can use a stage charger or a pulse charger to recharge the battery fast, but with a sealed battery valve regulated lead acid (VRLA) or absorbed glass mat (AGM) the charge rate needs to be carefully controlled.

With a 90 Ah battery using a smart charger rated 3.8 amp likely it will only charge at 3.8 amp for ½ hour, after which it will charge at a lower rate, and with a 35 Ah battery using a smart charger rated 3.8 amp likely it will only charge at 3.8 amp for ¼ hour, after which it will charge at a lower rate, so the difference in charge time is ¼ hour between the two batteries.

This
charge22-4-20.jpg
is typical of the charge pattern from a battery charged with a smart charger, you will note a very short time being charged at 3.8 amp = approx 58 watts, the meter measures watts the charger is using, then slightly longer at 3 amp = 52 watts, with the charge rate at 0.8 amp = 12 watts not being completed, it would have in fullness of time dropped to 0.1 amp and finally off.

Because most of the time the charge rate is very low, time to charge is rather long, this is why lead acid is not suitable for most electric vehicles, it was OK for fork lifts, milk floats, mobility scooters all always recharged at their base and used for less than 8 hours a day. But for cars, push bikes, etc, what the battery both light as possible, and ability to fast charge.

The AGM or VRLA can charge faster than flooded, but to do so the vehicle has to map the battery and hold the battery at 90% charge for a week but then allow full charge once a week to prevent battery damage, so it can only be done with computer control and with a vehicle in regular use. My wife's car with stop start with the lock down has required the battery to be recharged with a smart charger as used so little.
 
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The wife's car is not being used, so needs a charge this
Screen Shot All.jpg

Shows the first 3 hours, measuring input to charger so in watts, so starting at 12 volt so reasonably discharged, first 1½ hours put in around 6 Ah into a 90 Ah AGM battery, clearly very little, so now down to 0.8 amp charge rate, I would expect over night at least before it shows fully charged when charge rate drops to 0.1 amp, what you need to consider is how long would it take driving the car? I suspect a month, OK because wife has cancer and is not permitted to drive at moment it is not being used for rather a long time, have charged it once before during lock down, but 200 miles in 5 months is a very low mileage.
 
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