# Can I get 7A of current from two 3.5A rated batteries (without an increase in V)?

I have two variable batteries with the following specs: Li-polymer Capacity : 20000mAh / 74Wh Input (for charging) : DC 15 - 19V (1.3A max) Output : DC 12V / 4A DC 16V / 3.5A DC 19V / 3A

Now I have a Gigabyte mini CPU that comes with a 19V / 7A power cable. My intention is to make this CPU portable by providing it with 19V/7A using the batteries. Is there any way I could wire two of these batteries up to get my required 19V/7A? If I connect two batteries in parallel, I know the capacity doubles. Would that be able to provide what I need?

I'd really appreciate some help on this, thanks!

• Can you provide a link to the product? The specs you quote make it seem like a battery pack/DC-DC converter package, rather than just a battery. – Peter Bennett Jan 29 '14 at 0:14
• amazon.com/… It is a battery pack. I got a converter that splits the output into +ve and -ve. – lectron Jan 29 '14 at 0:18
• Assuming max power consumption at 19*7=133W. Your battery is rated 74Wh and charging at around 25W. Even if you manage to get it working with 2 batteries, you should expect just ~1hr of life and another 5~6hr charging – Pyxzure Jan 29 '14 at 1:45
• That's ok, battery life is not as important to me as getting the CPU powered properly for a period of time. – lectron Jan 29 '14 at 2:38

Technically yes.
Probably yes.
Possibly no.

Hard interconnection: The supplies will have diodes in the output so connecting foreign external voltage may be OK when it is operating and might be OK when it transitions from off to running. There is a possibility that the regulation / feedback does not like to see 19V on the output when it has not provided power and may not start.
Similarly, if one supply is set at say 19.1V out and the other at 18.9 V out,
Best case: the 18.9V supply sees 19.1V so concludes tha all is well so lays low. The 19.1V supply cannot supply the load and 'ags' until the 18.9V supply cuts in to take up the excess.
Worst case: The two supplies play 'pass the parcel' in some manner. the hv version is overloaded and start to shut down or completely shuts down. The LV version leaps in and is in turn overloaded. It shuts down and ...
But, it MAY "just work"

Series output isolating diodes: A Schottky diode or FET super-diode is connected externally to each of the supplies and the two diodes are commoned. Having a shared capacitor at the common point probably helps. I'd expect this to work well, but nothing is 100% when two control systems interact and each is not 'aware' that the other is there. Size of cap may make a difference. Larger reduces swings when serttling down. Too large may inhibit startup.

Adding a diode with say 0.5V drop loses 0.5/19 ~~= 3% = tolerable. The Gigabyte 19V input supply can almost certaionly to;lerate lower voltages than this.