Oct 17, 2015, 05:38 PM Registered User Miami Fl Joined Feb 2011 618 Posts Discussion 12v PB battery milliamp question I have a 35ah 12v AGM battery and want to wire another same battery in series to get 24v inpit to my charger. My question is if i do this will i get the same amount of milliamps to charge my 4s packs or will i gett more since higher input voltage lowers amp draw?
 Oct 17, 2015, 05:59 PM Registered User So. Cal. Joined Oct 2004 9,124 Posts Current draw will be roughly 1/2 as much so you will be able to get slightly more than twice as many charges provided both batteries are identical. If they're not absolutely identical, you would be better off connecting them in parallel.
 Oct 17, 2015, 06:20 PM Registered User Miami Fl Joined Feb 2011 618 Posts Will it still be the same amount of charges as using both batteries alone not in series?
 Oct 17, 2015, 06:28 PM Registered User Staffs, UK Joined Nov 2003 11,847 Posts It's going to depend on the charger and on what exactly you mean by "same amount of milliamps". If you mean CURRENT, which is what millamps actually measures then some but not all chargers will only produce the maximum output current with full input voltage. So if you've been running it on 12V you MAY be able to get higher charge currents with 24V input. If you actually mean milliamp HOURS, i.e. CAPACITY, then because you have 2 batteries you have twice as much energy (35Ah x 24V instead of 35Ah x 12V) so you can get twice the charge capacity e.g. charge more batteries. Steve
 Oct 17, 2015, 06:51 PM Registered User Miami Fl Joined Feb 2011 618 Posts Right that i understand let me see if i can phrase it differently. In example if i have 2 fully charged batteries and get 10 charges (each battery independently) until each 12v battery dies. Will i also get 10 charges from the same 2 batteries in series?
 Oct 17, 2015, 07:05 PM Registered User Joined Feb 2008 3,081 Posts Ignoring voltage efficiencies, 2 batteries will give twice as many charges as one battery regardless of how or if you hook them up. I know quite a lot of people think of amps as some kind of constant so the same number must be going in as coming out but it doesn't work that way when voltages are changing. Energy (watt hours) is conserved but not amps.
 Oct 17, 2015, 07:26 PM Registered User Miami Fl Joined Feb 2011 618 Posts So to sum it all theres no real advantage to connecting 2 batteries in series unless you want to increase voltage, i was thinking since in series the amp output would be less since the voltage is higher meaning more overall charges since less amps draws less power
 Oct 17, 2015, 07:34 PM Registered User So. Cal. Joined Oct 2004 9,124 Posts Again, two batteries will give you roughly twice as many charges as a single battery, whether connected in series or parallel. Given that current draw will be ~1/2 as much as when using the two batteries independently, you'll actually gain some usable capacity by connecting the two batteries together when powering your charger. How much additional capacity that you'll gain is dependent upon the quality of the batteries and the current draw. If you get 10 charges from one battery, you'll get 20+ charges when using two batteries (either in series or parallel).
 Oct 17, 2015, 07:44 PM Registered User Miami Fl Joined Feb 2011 618 Posts Ok got it thanks
Oct 18, 2015, 10:03 PM
Registered User
Joined Jan 2007
2,239 Posts
Quote:
 Originally Posted by flysohigh So to sum it all theres no real advantage to connecting 2 batteries in series unless you want to increase voltage, i was thinking since in series the amp output would be less since the voltage is higher meaning more overall charges since less amps draws less power
Another item. Putting both lead acid batteries in parallel makes it easy to charge them with a common 12 VDC deep cycle battery charger.

Putting both lead acid batteries in series requires you to disconnect the lead acid batteries from each other, and charge them one at a time. Yes, 24 VDC lead acid battery chargers are available, but hard to find, and likely a bunch of \$\$\$\$. (Or just charge them in parallel)
 Oct 19, 2015, 07:08 AM Registered User Miami Fl Joined Feb 2011 618 Posts Well i was just planning on charging them independently with my icharger
 Oct 19, 2015, 10:27 AM Registered User Joined Feb 2008 3,081 Posts iChargers can typically do at least 24V on the PB setting. Some can do 36V. So you have options.