# Safe Discharge Rate of Alkaline Batteries

I am working on a portable project. I need to pull 3,500mA average with 10,500mA peak at 3.6v-4.5v. I see that "D" Alkaline Batteries are rated for 1.2-1.5v and 12,000mAh. So I am looking at using a 3 "D" Alkaline Battery Pack to achieve the 3.6v-4.5v supply.

Question: 12,000mAh / 3,500mA = 3.43 hours is a reasonable amount for this project.

But, I have not been able to find anything on the maximum safe discharge rate of Alkaline Batteries. Is it possible and safe to pull 3,500mA average (and possibly 10,500mA at peak) from Alkaline Batteries?

If not, can I solve the problem by putting multiple battery packs in parallel?

Somewhat related (though answer pertains to AA batteries, not D): Short Circuit Alkaline Batteries

It looks like 3.5A might be safe for continuous draw and 10A is just about do-able during peaks, though I might be a bit worried that the internal resistance of the battery will prevent you from reaching the peak currents required, especially when the batteries are nearly dead. It will also vary from manufacturer to manufacturer, and possibly even battery to battery.

You can employ a similar solution to those used by camera flashes and other systems which have large surge currents: use capacitors. The lab down the hall from where I work uses them to discharge many MA (yes, mega amps) for extremely short time periods to provide high power bursts. Your low current supply can be used to slowly charge the capacitors up to the correct voltage, then when demand requires capacitors can be discharged extremely quickly because they have very low internal impedance. You'll need to size the capacitance as needed for however large the spikes will be. Keep in mind that some electrolytic capacitors have quite high ESR (an equivalent concept to internal resistance), and may have lower current ratings than what you'll require. Checking the specs/datasheets is always a good idea. Putting a current limiter between the battery and capacitors also wouldn't be a bad idea since shorting the battery to the capacitor is close to just as bad as shorting the battery itself (especially for larger capacitances).

Getting detailed data on capacity, safe discharge rates, life span and voltage discharge characteristics for most batteries from data sheets is nearly impossible. It seems as all the main stream alkaline battery manufacturers data sheets are little more than glossy marketing brochures with pretty colored pictures with extremely little hard data.

One wonders if they do this intentionally to keep customers from gaining expectations over battery performance that cannot be consistently met by the products.

Note that it has been my experience that you can get better data if you work directly with the manufacturer. I had previous experience with designing an NiMH battery pack with AAA cells. The industrial division of Panasonic was very helpful at the time of providing test data on their cells.

I note that battery makers e.g. Rayovac don't mention anythuing above 800 mA in their application notes. I'd take that as an indication the battery is unlikely to perform well for 10,500 mA peaks or 3,500 mA average continuous.

Some NiCd D-Cell batteries can be discharged at up to 5000 mA

High Rate Discharge(1C) minute ≥54 Standard Charge, l hour rest Before discharge by 5000mA (1C)to 1.0V/cell up to 3 cycles are allowed

If you are considering packs of D-cells (e.g. three sets of three) then you are into the same size and weight as a small SLA. They can easily handle higher currents - I'd consider using one of those instead.

Take a look at LiSOCl D batteries. You will need only 1 cell to reach 3.6V. for the current capacity, you might need 2 or 3 cells in parallel.