I got this APC from Amazon last year for my DS920+: https://www.amazon.com/gp/product/B01FWAZEIU

It works well, (have had minor flickering in power and the drive stayed fine) however my power went out for a while a few weeks ago and didn't shut down the DS920+ properly. I think it's because I didn't set up the shutdown correctly. Was $69.99 when I got it btw.

The exact unit you have pictured, no. my shutdown process takes about 5 minutes, you can adjust your shutdown time in settings. I'm using an APC I get about 19-22 min Battery time, we have issues in our basement where my wife trips the breaker so this is sufficient for me to be notified by Unraid (email) when on battery and go flip the breaker back assuming I'm home.

APC UPS, 600VA UPS Battery Backup & Surge Protector, BE600M1 Backup Battery with USB Charger Port, Uninterruptible Power Supply https://www.amazon.com/dp/B01FWAZEIU/ref=cm_sw_r_sms_apa_i_k4G8EbJH1TKR2

If it's in your budget ($80-$200 USD) I'd recommend grabbing a small battery backup, it'll also be handy for any other electronics like desktops. If the only thing you have plugged into it is the m3 max (125 watts) this one would last about an hour before shutting off but you can also get a smaller one like this if you only need 10ish minutes

If it’s otherwise working, why don’t you just plug it into a [UPS Battery Backup](APC UPS, 600VA UPS Battery Backup & Surge Protector, BE600M1 Backup Battery with USB Charger Port, Uninterruptible Power Supply https://www.amazon.com/dp/B01FWAZEIU/ref=cm_sw_r_cp_api_i_R5-7EbBYP9MYW)?

All rechargeable batteries degrade over time.