Lead acid battery gets pretty warm while filling up acid? What is the right voltage to charge it at CV?

Thread Starter

Rahulk70

Joined Dec 16, 2016
508
I recently got a Yuasa PowerSport (6N5.5-1D- 6V 5.5Ah) bike battery. Since, amazon does not sell it with the acid, it has to be purchased separately from a auto store or self prepared. I went with the later and prepared a 37% sulfuric acid solution using a 98% ACS H2SO4 reagent. If I'm correct flooded Lead acid batteries use 36-38% sulfuric acid electrolyte. I had prepared the acid solution yesterday. A little while ago I added the prepared acid to the battery and immediately upon adding the lead plates died/bubbled a bit and the battery is getting warm (not hot!). Is this normal or something is wrong with my battery?

The battery shows a voltage of 6.62V. While charging the battery for the first time can I use a constant voltage charger. Can the charging voltage be 7.2-7.5V like SLA or should it be lower for a flooded cell?
 

Ylli

Joined Nov 13, 2015
965
Sounds like a bit high on the acid concentration. Assuming you are using 18.4 molar H2SO4 with a density of 1.84 g/ml, then a 30% solution with water (density 1.0g/ml) should give you a final SG of just over 1.25. After initial charge, that may increase a bit. Don't see anything about SG on the battery specs, but generally anything over 1.25 is undesirable in regards to battery life.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
508
Sounds like a bit high on the acid concentration. Assuming you are using 18.4 molar H2SO4 with a density of 1.84 g/ml, then a 30% solution with water (density 1.0g/ml) should give you a final SG of just over 1.25. After initial charge, that may increase a bit. Don't see anything about SG on the battery specs, but generally anything over 1.25 is undesirable in regards to battery life.
Thank you for the update. I contacted Yuasa and the engineer told me that I can use anywhere from 36 to 38% acid concentration. That is around 37.57mL of acid for preparing 100mL 37% acid solution I guess?
 
Last edited:

jpanhalt

Joined Jan 18, 2008
9,785
Yes, that is correct. Be sure to add the acid to water, not the other way around. Then after you have approximately (but less than 100 mL) of cooled solution you can carefully adjust to final volume with water.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
508
Yes, that is correct. Be sure to add the acid to water, not the other way around. Then after you have approximately (but less than 100 mL) of cooled solution you can carefully adjust to final volume with water.
Yes, I have to constantly run chilled water around the glass vessel I'm preparing the solution in. It's a long process mainly due to the enormous heat this thing generates. Especially if you have to prepare for a large battery that required a liter or more.

Oh yeah, other way round water into such a large quantity means RIP to face and eyes!
 

drc_567

Joined Dec 29, 2008
855
... use distilled water. Tap water often has a high mineral content, which may enter into the chemical reaction somehow.
 
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