Cordless string trimmer batteries...two 20v vs one 40v, which is better?

[dennis thompson]

I am looking to buy a cordless lawn string trimmer/edger for my small yard. I probably can trim/edge the lawn in about 20 minutes. One trimmer offfers two 20v batteries while another (same price and brand) offers one 40v battery. I kind of like the idea of 2 batteries...if one goes bad you still have the other.
Any thoughts/comments/experience will be appreciated.
Thanks

[George Bokros]

I believe the amp/hr rating is the way to tell how long the charge will last.

Here is something that may help

https://www.essentialhomeandgarden.c...battery-guide/

[Derek Meyer]

I have the Dewalt 40V string trimmer with the 4.0Ah battery. It is easily as powerful as my old gas string trimmer, and lasts about 40 minutes on a charge, which is more than enough time for me to trim my whole lawn. It's heavy but well-balanced - I can use it with one hand if I have to. I also bought the 40V leaf blower so I have 2 batteries and 2 chargers.

They offer a 6Ah battery which should last about an hour on one charge, but none of my local dealers had that one in stock.

[Carlos Alvarez]

I have the Dewalt 40V string trimmer with the 4.0Ah battery. It is easily as powerful as my old gas string trimmer, and lasts about 40 minutes on a charge, which is more than enough time for me to trim my whole lawn. It's heavy but well-balanced - I can use it with one hand if I have to. I also bought the 40V leaf blower so I have 2 batteries and 2 chargers.

They offer a 6Ah battery which should last about an hour on one charge, but none of my local dealers had that one in stock.

Something about that math seems odd, because that would suggest that you're using 1/3 of a HP to run it. Most gas trimmers are a bit over 1HP. Do you just never run it at full power?

As far as the original question, two 20v batteries isn't necessarily different from one 40v. You still need the full 40v (unless it's a very low-powered tool). The only variable would be total capacity, translating into runtime. Let's say you can have one 40v with 4aH capacity, or two 20v with 6aH each. Well now you have 50% more capacity in the tool. When run in series, you double the voltage but the capacity stays the same. This is how most tools operate. It also means you always have to have both batteries.