I have had the luck to test quite of few of the high voltage (36-56v) chainsaws to be able to actually measure their true output power, chains speed, battery impedance, etc. I was not concerned about actual cutting ability since that is so dependent on the chain and a fairly arbitrary measurement. I got involved in this because as part of my work I have built several cordless chainsaws (before any higher volt models were available) for specific scientific use and have been looking for "off the self" unit to use. About the only saw I have not seen yet is the Husqvarna 536 cordless (so far too much money) though I have been able to piece together some information on it.
When I say true power output, it is a function of a couple of things. One is the internal impedances of the motor, electronics, and battery; the other is the "safety" limit built into the electronics. In all cases so far the internal safety limit of the electronics limits the power below the max efficiency point for the combination of motor/electronics/battery. The higher the efficiency to longer the given cut time for a set of batteries. Why do they limit the power to the motor? To protect the batteries and electronics.
On the subject of brushless versus brushed motor, brushless wins hands down for power/weight/efficiency. With the proper setup, brushless motors can have a fairly broad 85% plus efficiency band. With brushed motors in these tools, you a lucky to even hit 85% peak efficiency, more likely in the mid 70's. Since the brushed motors are much less efficient, you have to use extra power to provide cooling to the motor. For example, the Makita 36v chainsaw uses a brushed motor and it consumes about 70 watts of power to cool itself. The Stihl MSA 160 brushless motor uses about 20 watts of power for cooling. Also, the brushless motors have a much lower impedance. The Stihl MSA motor has an internal resistance of 0.03 ohms. The Makita 36v chainsaw has an internal resistance of 0.31 ohms (one of the primary reasons for lower efficiency). The higher the resistance the higher the losses.
Another big issue is the impedance of the batteries. Higher impedances in the battery increase the self heating of the battery and drop the overall system efficiency. The big name brand companies use high discharge rate batteries with low internal impedance. Most of the cheap Chinese use higher capacity cells which have lower discharge rates and higher impedances. The companies that use the high discharge rate battery cells are Stihl, Makita, and surprisingly Ryobi. The EGO, Oregon, and Greenworks use higher capacity cells which have higher impedances which lead to more losses and battery self heating. On higher impedance cells, the manufacturers limit the current from the cells to prevent them from destroying themselves. Lower current means lower torque. So a good indicator of the discharge rate of the battery is the chain speed. The manufacturer trades lower chain speed to get more torque (speed times torque is power output) so you don't stall easily.
For example, the EGO (chain speed about 1200 fpm) lithium cells can be discharges at 3 times their capacity (3C) safely. So the manufacturer limits the current output of the motor controller to 12 amps (3 times 4 amp-hr). So given that the battery voltage of the EGO is 48v (I know, the 56v is the max charge voltage), the max draw from the cells is about 600w. Give the losses in the batteries, controller and motor, the max power to the chain is only about 450 watts, or about 0.6 hp.
In comparison, the Stihl and Ryobi brushless chainsaw batteries are high discharge rate (10C). Chain speed on both is 2000-2200 fpm. The electronics current limit on both kick in at about 25 amps (6C for a 4 amp-hr pack). So given they both have 37v battery packs (42 volt max charge voltage), they can both draw 970 watts from the batteries. With the lower impedance cells, the losses of the batteries is less so the max chain power delivered is close to 800 watts (about 1.05 hp) even though the battery voltage is less than the EGO. The efficiency at max power is close to 85%. It would actually peak at max efficiency of 90% at about 34 amps which is beyond the electronic limit of the controller.
So what does this all mean? Higher chain speed seems to indicate a lower battery impedance which in turn indicates a higher efficiency/better quality. Don't bother with a brushed motor chainsaw due to the lower efficiency. The Makita 36v chainsaw is a nice durable, light saw but the max power chain output is only about 500w as I measure it and its max efficiency is only 70% due to the large amount of cooling and an high internal resistance of the motor.
If I can figure how to do it, I can generate a table and put it in this discussion of chain speed, max power, etc. It appears that the real bargain chainsaw out there is the Ryobi 40v (actually 37v) brushless chainsaw. At $200 for the chainsaw with battery and charger it performs as well as the Stihl MSA 160. It uses a standard 3/8" Pico chain so you have a large selection of chains available. Originally the Ryobi came with a 4 amp-hr battery but now it seems to only come with the 2 amp-hr as standard. If you can live with the Ryobi brushless chainsaw not having a chain brake it is good buy.
