Bose Soundlink Mini 1 Speaker: Extending Battery Life with Powerbank & USB Charging Options

Hello community, I have been tackling an issue that bothers me for a long time, but one by one. For several years I have been a happy user of the Bose Soundlink Mini 1 loudspeaker, but with age, its built-in battery wears out more and more and now it can withstand about 1/3 of the time of its youth on one charge. There would be no problem if it was possible to charge it with a powerbank via USB when you are somewhere out of town on a barbecue, but in this model there is no possibility of charging via USB 5V (this convenience was added only in the second newer version of this device, but neither I dream of replacing it with a newer one when I am so happy with the currently owned speaker ... that's just charging ...) You can only charge it from a socket (or a car cigarette lighter) using a dedicated 12V 0.833A charger (photos below). I have a 15,000mAh powerbank at home with USB outputs: 1x 5V 2.1A and 1x 5V1.0A and here is my idea to try to use it to charge this speaker during trips outside the city. The problem is the difference in the necessary voltage - the speaker needs 12V and the powerbank gives 5V and you need to find the right cable on one side with a USB output and on the other side with a DC output - so that it fits the speaker (photo below). I looked around a bit and found several cable models with a 5V to 12V converter and a DC tip mounted immediately:

PS. Sorry for the lack of direct links but I am new here and I cannot put them correctly.

1: amazon.de/product-reviews/B009AM2X04/ref=cm_cr_getr_d_paging_btm_3?ie=UTF8&reviewerType=all_reviews&showViewpoints=1&sortBy=recent&pageNumber=3

2: ebay.de/itm/5-5-x-2-1-mm-USB-5V-to-12V-dc-Connector-Step-up-Module-Converter-Male-lead-cable-/282394281690?var = & hash = item41c002c6da: m: mvx3QE4oV7jQnF4q1BeDkEQ

3: amazon.de/Kingwon-USB-Stromkabel-Konverter-Boost-Linie-DC-USB-Anschlusskabel-Schwarz/dp/B01IM3FNPI/ref=sr_1_2?ie=UTF8&qid=1494525983&sr=8-2&keywords=us%b%2Bd 2B12V & th = 1

4: amazon.de/dp/B01ID90K4A/ref=sr_1_3?s=ce-de&ie=UTF8&qid=1494470628&sr=1-3&keywords=5v+12v+usb

I got to the comments about the first 3 cables and people there complain about the charging speed, so I would prefer option 4, but here are my questions:
- if I connect the converter No. 4 to my powerbank to the 5V2,1A socket, how many 12V amps will come out on the other side of the cable?
- if there is more than 0.833A at the output, will the loudspeaker burn out? will the battery burn?
- I know that in the case of the first 3 converters, people use the USB Y connector (photo below) to increase the current, is it also necessary if I decided to use converter No. 4?
- does it even have a chance to work?

I know very little about the electronic trade, so I would be happy to hear any advice.

best regards

So on quickly-
At the output you will not "get" any amps, you will get as much as the receiver takes.
5V * 2.1A = 10.2W this power can be provided by your power bank. 12V / 10.2W = 1.18A, so it should be enough, ignoring the losses.
The only question is how the battery is charged in the loudspeaker, I will not tell you that. It is not known whether the power supply is stabilized.

Most likely there are two 18650 cells sitting there, it results from the photos.
It will be cheaper to replace the cells with new ones with a higher capacity.

If previously the playing time was satisfactory, then after replacing the cells with some 3000 / 3400mAh - it will be much longer.

Without combining and carrying powerbanks.

If it were so, you can buy 2 Efest 3000mAh cells for less than 10 EUR.

In the end I chose "KUNCAN Dc 5v to Dc 12v Converter"
http://www.ebay.de/itm/KUNCAN-Dc-5v-to-Dc-12v...6285?hash=item465d8212bd%3Ag%3AnBsAAOSwRYl6VR

It heats up slightly but charges the speaker properly