Is it worth buying 66i because of battery type?

All inReach devices have a LiIon battery which cannot be replaced by the user. Once it reaches end of useful life, Garmin will service it (most likely, swap it with a refurbished unit) for a fee. You can probably find instructions for replacing it yourself - as well as third-party compatible batteries. However, this will void your remaining warranty (if any). And you run the risk of damage to things like the water-tight seals even if you have no problems with the electronics.

If you like rechargeable batteries, you can use them in any Garmin handheld. However, they will not recharge IN the unit. You need an external charger. 

Judging from the forum traffic, most people seem to prefer the standard form factor replaceable batteries (AA or whatever) over the non-replaceable LiIon. Most of that discussion seems to center around either (a) the finite life of the non-replaceable battery or (b) the fact that I can't carry and use spare batteries - I have to lug a backup battery pack or solar charger.

https://m.youtube.com/channel/UCtkNsX-BwK0IOr6Rta8onuA

I agree with Twolpert on many part of his post . Personally I will buy a multi gnss unit (Wich 66i is not) with AA batteries and I reach mini . Here you can see how change the li ion battery Wich is sales on the web .

Thanks. So it seems to be very easy to replace the battery on your own. The bigger problem seems to get the replacement.

AliExpress sales ir with the back cover included in the color that you want. Also (when you reach the point of damaged battery) you can measure with a tester and go to a battery center for replace. The only part that I will add (Wich video doesn't) is before putting back cover again , I will add silicone seal just in case. The rest , easy cake

Remember that charging a Garmin Outdoor GPS with a power banck or solar charger , is just simple as put a thin plastic layer pressing the switch between the batteries , and ready. This is the same that official battery pack(of course use rechargeable batteries)

I'm waiting to hear from Garmin as of typing right now but my 66i does not charge from my Falcon 21 solar charger.  It puts out 21W at 2A max and isn't enough juice.  The computer usb is also failing to charge.  It seems to only work on direct AC.  Well, that's pretty worthless for me.  I need my unit to last for several weeks in the Canadian bush.  If it isn't rechargeable by solar then it's a really really expensive canoe anchor.  It's going back to REI!  I'm getting a Zolio and sticking with my trusty Garmin 450t for navigation support.  I can always count on swapping out batteries.  Don't know why Garmin has to change something that works great!!!

I think there is something wrong with your 66i- maybe the cable is defective? I am able to charge my 66i via a power bank.  Haven’t tried a solar charger, will do if there is sun available in the next days.

forums.garmin.com/.../gpsmap-66i-and-external-battery-pack-charger

I agree with Volker on this one. The only thing I would add is that the current state of charge on the 66i itself might matter here. If the device is close to fully charged, it MIGHT be that the unit draws insufficient current to keep a battery pack "turned on". I have packs which shut down in this way because they assume that low current draw means fully charged. So you might want to retest with a 66i which has a relatively low charge (e.g., 50% or less).

I have no idea if the same thing applies to a solar charger. Don't have one.

This is certainly not due to "not enough juice". The device itself determines how much current it draws during charging. I don't remember the details, but the device determines the capacity of the source and draws accordingly. No matter what it finds, it will draw 500mA at a minimum.

More likely, the charging device is shutting down because the unit is not drawing enough current. If you have not already done so, you might want to rest with a discharged device (say 50% charged or less).

Reason folks buy unites with SOS and text messaging capability is to be used in remote area and for extended time, like back country hiking, camping, hunting.

Having a unit with the chargeable battery does not serve this purpose very well,

I stopped by Costco and bought big pack of batteries and I don’t have to worry about running out of battery or have to carry solar charger which may or may not work especially in rainy days.

i’m completely at lose that some user on this website like rechargeable battery. I guess if I go to New York Central Park camping  I don’t have to worry about that.

SOS and messaging capability via Satellite is a fantastic option which can save lives, and sadly Gahreman ruined it by having devices with the rechargeable , battery,.

I do have a 66i  but I use it only for Messaging because of lousy battery inside and I use my older version for GPS which is regular battery operated with no hesitation, since I don’t have to worry about running out of battery,

A great idea and future has been downgraded due to  power requirement in the device,

I hope either GARMIN comes up with a new device that takes regular battery or another company do so with the same capability,

Unfortunately, this is not possible. The Iridium modem draws a lot of power, especially when transmitting. No battery chemistry other than LiIon can provide sufficient power. Does not matter if we are talking about disposable alkaline, disposable lithium, or rechargeables such as NiMH.

There is only one iR device with a removable LiIon battery pack. That is the Montana 7x0i. However, the Montana is not really suitable for backpacking use. It is huge and ridiculously heavy. In addition, it’s unreliable. Shuts down randomly. Garmin has been working on that problem for over three years. Can’t seem to fix it.