Yep, that's what I did.
Get the Black & Decker 40V and it's handy for traditional use as well as clearing deadfall on the trail (especially that which is not winchable because it is actually amongst the trees).
The 20V option is OK, but it's not as capable, but would likely be handy in a pinch if you know how to operate one for larger trees.
I have always carried a Bow Saw (or two) and a Double Bit axe (that way it goes longer between sharpenings and is a back-up if it hits a nail or something) and a hatchet. This is especially handy for winter off-roading which is prone to uncleared trails covered in ice-storm deadfall. However, after 2-3 in a row you're gonna want a chainsaw, especially versus sweating it out either in too hot or too cold weather, and especially with all the dust and crap around. And with bigger trees it nice to be able to work below with some confidence, versus trying to get a bow saw to do that is a pain and on larger elevated trees where it's not an option of just working from above or the sides without switching between saw and axe.
Last year while off-roading in Montana I came across 3 fallen full-size trees (between 10-18+inch diameter) and a few fallen saplings crossing the trail deeply embedded among the other trees on either side of the road. After the second one I was wanting my Stihl (or even the old Jonsered).
I'm not a fan of having gas chainsaws in the vehicle (much prefer it in the bed of a truck), so I went looking for a good, capable and relatively inexpensive electric chainsaw. Now buying a 1250-2000 amp inverter to hook directly to the alternator and then a typical electric chainsaw was one possible route, and about the same cost of a gas or battery option. However the hassle versus utility was the limiting factor, and it also didn't offer the option to take it up the race course and use it there, or while hiking.
I thought possibly of using one of my cordless reciprocating saws with a 12" HD 4TPI blade or pruning blade, but from past experience with even finished lumber (let alone sappy/dirty trees), they aren't as quick as a chainsaw and get dull and bind quickly enough.
So I started looking at battery options. After looking at the Home Despot's house brand like ION and a few others, and even the higher end models like Makita, I decided the B&D one seemed to be the good balance of utility and price. It is not the best, and of course it would be nice to have some features of a gas or corded model, like a real chain brake, but it is very handy and for me it's proved to be a good investment.
I would recommend doing your own research to see what is a best fit for your need. Also I'd recommend choosing the higher voltage model if it's just a small premium, as that extra juice pays off especially on larger diameter trees. The typical 18-20V models are for pruning essentially, but can be used to remove larger diameter trees if you know how to tackle them, but they do tire quickly and are noticeably weaker than the 40-48V models.